Hill Daddy

Thinking I had the sound narrowed down to the rear diff, I pulled the cover to inspect it. The fluid was a clear amber and there was only some smooth, putty-like build-up of very fine metal particles on the magnet. No real slop or other problems found and everything looked OK. However when reviewing the pics I took more closely, I saw what looked like serious wear on the ring gear. So yesterday I had it in a reputable local shop and their drive train guy said this was "normal". I have to believe him since this is what he does and this is a serious truck town. He checked the backlash, said it was in spec and there were no problems with the differential. He also drove the rig and was only able to duplicate the sound once, very briefly (naturally). He also thought it was coming from the front which it does sound like from inside the vehicle, but from the outside it clearly sounds like it's coming from the rear (maybe not though). He also agreed that any sound coming from a drive train component should vary with speed, which this does not. His suggestion was to "drive it til it fails". So basically he's stumped, and threw in the towel. On the upside I suppose they could have charged me for a new ring and pinion, and I'd still have the noise. As it was I walked away with more questions and a "free" $158 car wash. On one hand I'm kinda relieved that this problem is kicking everyone's ass, not just mine, but I'd rather be a dumbass and have it fixed.

It's definitely in back. Had my son drive it today in an empty parking lot while I watched/listened/chased on foot. We finally found a pot hole that usually set it off when the right rear wheel rolled over it. Couldn't tell for sure but sounded like the middle rear area so probably the the rear diff. Still really strange that the noise is constant regardless of speed but there's nothing left back there to check other than the differential. At least I know what I'm in for when I take it in. Will post a follow-up report since I'm dying to know the root cause. I'll make sure to ask for the bad parts. Thanks all for the suggestions.

So I pulled the left rear rotor to inspect. Nothing rubbing on the dust shield. Did find one problem but doubtful its the source of the noise. The E-brake shoe is completely worn to bared metal. Oddly not shiny metal, just no pad material left whatsoever and dirty/rusted. Also inspected the exhaust, driveshaft more closely while I was under there. Nothing found.

Scratch one more suspect off the list. Just disconnected the EVAP vent solenoid and it still makes the sound. While I was under there I also inspected: > E-brake cables,- nothing rubbing or loose > Both rear dust rotor shields (without removing wheels) - no signs of rubbing or looseness. , > Jostled the exhaust system by hand - no rattling or loose brackets. > Driveshaft - nothing rubbing or anywhere near contacting Running out of ideas but have a few additional notes; The sound (sometimes) seems to be set off by turning, either left or right, but also happens when moving straight. Road bumps definitely trigger it, but can't tell if there's a specific wheel that is more sensitive than others. Will try pulling the right rear wheel tomorrow to inspect the rotor, e-brake. Beyond that it's looking like a trip to the dealership.

The sound does have a plate-like quality to it and a dust shield seems plausible. I would think something like a dust shield would have a relatively fixed resonant frequency. Might only take a small point of contact with the rotor or an object between to make it rattle the same at different speeds. Adding that to my laundry list. Thanks

Thanks muddkatt, Ironically, this happened on my way home from work Monday morning. Made it home, pulled the left front wheel and found the caliper completely loose. Both bolts had worked out over the last 2 weeks. Swore I torqued them down tight but apparently not. Lesson learned there. Amazingly no apparent damage and brakes seem fine after putting in new caliper bolts. What really sucked was that I missed an appointment at the local Caddy dealership to check out the noise problem. I'll be pulling the right rear wheel today and that will be one of the first things I'll check.

Hello all, My apologies for skipping a proper introduction and straight into dumping a nasty problem here. Unfortunately, I'm about at my wits end with this and hoping someone here might know what the ____ is going on with my rig. I've searched extensively online, discussed with automotive knowledgeable friends/family, and even had an online discussion with a certified Cadillac tech. Everyone is stumped. I'm ready to sell or trade it in at this point but nobody would buy it. The short story: A loud, intermittent, vibrating/oscillating/growling noise coming from somewhere in the rear, driver's side area of the vehicle. Originally I thought it was drivers side front so much of the below troubleshooting was mis-directed there. I'm including that info to cover all the bases. Anyway, I FINALLY caught it making the sound in the driveway yesterday and got out so I could hear it with my wife behind the wheel (only does it when moving -even extremely slow). The sound is difficult to describe but has a growling/grinding/vibrating quality to it, that changes very little with speed or engine RPM. Unfortunately it has gotten worse in the past few days, to the point I don't want to drive it during daylight hours it's gotten so embarrassing. I did find one youtube vid that recorded the same exact sound. Skip to the 2:00 mark to hear it: 2005 Chevy Silverado Front End / Axle Grinding Noise... NEED TO FIX. Unfortunately the OP claims replacing the wheel hub fixed the problem. I just did that last week with no luck. Troubleshooting history: Originally, I thought the problem might have something to do with the ABS unit "misfiring" since the noise sounds like something being activated/de-activated, versus a purely mechanical grinding/contact type problem. It does NOT sound like any bearing noise I have ever heard. When I found the video I was skeptical it would be the hub until I looked up the part and found that a new wheel speed sensor is part of the assy. My thinking then was that the wheel speed sensor was somehow causing the traction control to kick in/out rapidly. Again, basically a control loop problem versus a purely mechanical one. Unfortunately pulling the ABS fuse, replacing the front/drivers side hub, and now disconnecting both front wheel speed sensors has had not made the noise stop. I still have a few ideas but would love to get some input from anyone with experience with GM AWD systems. Here's what I can say about the problem: 1) It's a loud, intermittent, noise from somewhere in the left rear (sounds like wheel well area) of the vehicle. 2) The noise will usually cut in/out in very rapid "bursts" but will occasionally "stick" on until the vehicle comes to a complete stop. 3) It is almost always triggered by road bumps, or variances in road roughness. Sometimes very minor, and at very low speed. 4) The noise only occurs when the vehicle is moving. Even at walking speed or slower, but ceases once at a complete stop. 6) It does NOT sound like bearing noise. "Metallic, hollow, oscillation, vibrating, growling" are descriptors I would use. 7) Other than a slight drop in frequency (pitch) when slowing to a stop, the pitch of the noise is constant, and independent of speed or engine RPM. If I had to guess I'd say it's in the ballpark of 40Hz. 8) The amplitude (loudness) does change slightly with speed, but only quiets slightly just before coming to a complete stop. 9) The noise seems "externally powered". As though something is being "activated" electrically, pneumatically, or hydraulically. I say this because the noise seems much louder than it should when moving very slowly. Almost like being driven by a motor or solenoid. 10) There is no apparent feedback that can be felt in the steering wheel, brake pedals, handling, braking, acceleration, or ride of the vehicle. Just noise. Here's what has been tried with no success: 1) De-activating ABS by pulling the fuse. 2) Cleaning the drivers side front wheel speed sensor (possibly some improvement but hard to tell given the random nature). 3) Replacing drivers side front wheel hub (fix per youtube video with EXACT same sound). 4) Disconnecting both front wheel speed sensors. 5) Putting the rig in Neutral, and reverse while the noise is happening (still does it). 6) Pulled the left rear hub/rotor to inspect the E-brake - looks/feels OK other than being worn and dirty. Did feel some slop in the axle changing directions when rotating by hand but not sure whats normal. 7) Disconnected the rear suspension compressor 8) Pulled the VSES/ECAS fuse to disable the suspension damper solenoids. 9) Also pulled the 4WD fuse in the instrument block - just because. Not much left to try without digging into the drivetrain innard$ but really confused as to why the tone/frequency of the sound is relatively constant regardless of whether I'm driving 50mph or 5mph. It does quiet somewhat and drop slightly in tone at very low speeds (like 1 foot per second). The fixed nature of the sound makes me think its some kind of resonate frequency as opposed to gears etc... Maybe the plates in the viscous coupling are slipping/vibrating????? The only other thing in that area of the rig I can think might be causing the problem is the EVAP solenoid????? Cant imaging that would be loud enough to hear 2 blocks away. This is really starting to get on my nerves. The rig is drive-able, but the noise can be really bad, and is hugely embarrassing at the wrong time. Like when leaving a track meet Thursday night with tons of people on the sidewalk staring, and some laughing (maybe not the best idea to mock someone that's stressed out and driving a 7,000# SUV - just say'n). Pretty much hit a wall and ready to take it in (cringe) unless someone can enlighten me here. THANKS!!! EDIT: Here's a video I took this afternoon. The sound can be heard several times. Fortunately I only cursed once (don't watch if the "S" word offends you).