'07 Sierra Transmission Knock/rattle

[chevydriver37]

Hi all,

 

07 Sierra, 5.3L GMT900, 4x4, WT, 53K miles. Some background: I've had a ticking/knocking noise on cold and warm start for about a month now. Noise is more prevelant at cold start than warm. Thought it was the AFM lifters acting up, or the dreaded piston slap gone terribly bad.

 

The noise has gotten progressively worse, and sounds almost like a rod knock. To say the least, it's LOUD. If I step on the gas, the noise quickens with the increase in rpms. It goes away between 15 seconds and 2 minutes after start, warm or cold.

 

Had the truck on the lift yesterday doing front brakes, and asked techs to check it out. One thought it sounded like one of the exhaust heat shields rattling. Another tech thought lifters. So, with remote start in hand, we started her up and shut her off about 20 times, listening with a THEBIS (snap on's stethoscope).

 

Come to find out, the noise is in the tranny - or that's at least where the noise is the loudest. It goes away as the engine/tranny warms. Also, the noise isn't as loud if you stand directly under the engine as opposed to standing under the xfer case/tranny.

 

I've done a lot of searching here in the forums, and don't see any posts with this issue, or any TSBs, etc.

 

Does anyone have any ideas on this, or even heard of this before? Before I take in for warranty service, I want to make sure I point them in the right direction.

 

Thanks

Rick

[silent_h]

I have been looking for someone with this problem for 2 months now. My truck is 2 months old (2010) and it definitely makes this noise you speak of.

 

Besides hearing it at start up is it only prevalent when your accelerating?

 

My problem is when I take the tech out for a drive he can never seem to 'hear' the same noise I'm hearing.

[chevydriver37]

I have been looking for someone with this problem for 2 months now. My truck is 2 months old (2010) and it definitely makes this noise you speak of.

 

Besides hearing it at start up is it only prevalent when your accelerating?

 

My problem is when I take the tech out for a drive he can never seem to 'hear' the same noise I'm hearing.

 

My writer didn't hear it either. That's the p*sser of this problem; it was intermittant at the time, but does it all the time now. It first started out as clicking, and got progressively worse. That's why I thought it was the AFM lifters acting up.

 

If yours is like mine, it'll get worse, but the noise goes away with acceleration and as the system comes up to operating temp. We stood directly underneath the vehicle and checked it, like I said, at least 20 times. All the noise seems to be coming from the tranny.

 

I searched all over the place for TSBs, and others who have the same issue, with no luck. I'm hoping that others chime in here that have the same issue.

 

Rick

[bell_man]

I have been looking for someone with this problem for 2 months now. My truck is 2 months old (2010) and it definitely makes this noise you speak of.

 

Besides hearing it at start up is it only prevalent when your accelerating?

 

My problem is when I take the tech out for a drive he can never seem to 'hear' the same noise I'm hearing.

 

My writer didn't hear it either. That's the p*sser of this problem; it was intermittant at the time, but does it all the time now. It first started out as clicking, and got progressively worse. That's why I thought it was the AFM lifters acting up.

 

If yours is like mine, it'll get worse, but the noise goes away with acceleration and as the system comes up to operating temp. We stood directly underneath the vehicle and checked it, like I said, at least 20 times. All the noise seems to be coming from the tranny.

 

I searched all over the place for TSBs, and others who have the same issue, with no luck. I'm hoping that others chime in here that have the same issue.

 

Rick

 

 

Sorry it took so long to reply. Mine turned out to be the catalytic converter. They replaced it have not had any noise since. Good Luck.

[ken1mod]

Check the torque converter to flexplate bolts. This can make an unbelievable racked. Cheap and easy to check.

 

Ken

[chevydriver37]

Check the torque converter to flexplate bolts. This can make an unbelievable racked. Cheap and easy to check.

 

Ken

 

Thanks Ken. Truck just threw a P0420 about an hour ago. My little MAC Tools code scanner doesn't give any other info other than "Catalytic Converter System Efficiency Below Threshold - Bank 1". Plus I got a B2A00 and B2AAA, which obviously aren't supported by that scanner. Guess maybe I misdiagnosed this for transmission noise?

 

Off to the dealer I guess...

 

Thanks again

[chevydriver37]

Check the torque converter to flexplate bolts. This can make an unbelievable racked. Cheap and easy to check.

 

Ken

 

Thanks Ken. Truck just threw a P0420 about an hour ago. My little MAC Tools code scanner doesn't give any other info other than "Catalytic Converter System Efficiency Below Threshold - Bank 1". Plus I got a B2A00 and B2AAA, which obviously aren't supported by that scanner. Guess maybe I misdiagnosed this for transmission noise?

 

Off to the dealer I guess...

 

Thanks again

 

 

Advised was a bad cat and O2 sensor. All fixed, picking up today. Thanks for replies and advice; as always it's appreciated!

 

Rick