Odd Sound From Under Hood...

bassadict69 · December 17, 2007

I cannot tell what exactly it is that is making the racket, but if it is a cold morning, something under the hood makes some squeeking sounds for a few minutes until it warms up a little.

It isn't constant like a belt squeeling & doesn't really sound like a belt, it is more of a squeek sound.

Any ideas what this is?

VMax2007 · December 17, 2007

I cannot tell what exactly it is that is making the racket, but if it is a cold morning, something under the hood makes some squeeking sounds for a few minutes until it warms up a little.

It isn't constant like a belt squeeling & doesn't really sound like a belt, it is more of a squeek sound.

Any ideas what this is?

I noticed that too. I am pretty sure it's an Alternator bearing. I am keeping an ear on mine. On real cold mornings it squeels a VERY high pitched squeel, but not like a typical belt or power steering squeel. More like steel-on-steel. Then even when warm, open your hood and listen very closely while idling, near the alternator. You can hear the bearing noise slightly. I am waiting for mine to become worse and more consistent before bringing it in. That way it will be easier for them to replicate. Otherwise I will have to leave it overnight on a very cold night so they can hear it upon cold-startiing. Don't wanna do that.

Darkanion · December 17, 2007

I cannot tell what exactly it is that is making the racket, but if it is a cold morning, something under the hood makes some squeeking sounds for a few minutes until it warms up a little.

It isn't constant like a belt squeeling & doesn't really sound like a belt, it is more of a squeek sound.

Any ideas what this is?

Maybe a bearing on a pulley or tensioner starting to go out?

I know you said it's only on cold mornings. But, I'd suggest popping the hood, when it's making the noise. Then, move back & forth in front of the truck, looking at the truck, to figure out where it's coming from. "Is it more the top than the bottom?" "Is it more the left side than the right side?" Once you kind of figure out what quadrant or area it's in, get a little closer and turn your head from side to side. You should be able to isolate it down to some "thing" to have checked or to check out yourself.

I seem to remember hearing about people using a straw from an old style straw boom (not the ones made from plastic). Grip the straw between your index finger and thumb. Then, touch each thing you think could be making the sound. You should be able to "feel" the vibration of the sound through the straw. From what I remember (it's been a while, since I was exposed to that technique), that usually works better on 'ticking' sounds, but it might still be useful in this scenario, too...

EDIT : OH, yeah! Be sure to keep safe distances from moving parts, etc. Also, if you go the broom-straw route, you touch the "thing" that could be makinb the noise, not the pulley itself. Good luck!

jrrod2004 · December 17, 2007

same here, did it bad this morning and I will be taking mine in for service tomorrow, will let yall know what they find (it does it when the tach is above 1000 but below 4500 so they should be able to replicate the problem fairly easily)

Nytemare · December 17, 2007

I have it too, I think its the fan clutch. Could also be the belt tensioner where everything is cold and the belt slips on it, or any other of the pulleys.

It only does it in the cold, never when its above 50*

ChrisNJ · December 17, 2007

My 6.2 has a very high pitched but very feint whistle at idle in drive, goes away upon accell after about 1K rpm. if i have the radio one i don't here it. put it in N and is still there, so it's the engine for sure. do we all share the same alternator in the nbs trucks?

jrrod2004 · December 17, 2007

I think there was a TSB for this, but I cant remember where I saw it or what platform it was for.......(still looking)

ws6_guy · December 17, 2007

Last month mine started making this sound, and on Saturday night my power steering pump failed and shot and its in the shop now...

WFO · December 17, 2007

My guess is it is the mass air flow sensor. Mine makes that noise when it is cold at start up.

bassadict69 · December 17, 2007

I wonder if I can record the sound on my cell phone then send it to email & save on photobucket or something? I may try that in the morning so I can post the sound...if it is cold enough in the morning!

2007silveradonbs · December 17, 2007

That is the same issue I have. It was diagnosed as my PS pump at the dealer and there is currently no fix for it.

bassadict69 · December 18, 2007

Well, got up this morning & carried the digital camera out when I went to crank the truck. It wasn't as cold last night, only about 33 or 34 so the truck made absolutely no noise this morning when I cranked it up.

It may be another week before it is cold enough again...our highs are supposed to hit the 70's again in the next day or so, so the night won't be anywhere around freezing!

08 Sierra Z71 · December 18, 2007

Neighbor's cat? Sorry, couldn't resist.

07SLT · December 18, 2007

I have the same high pitched prob on cold startup with my 07 NBS 5.3. I also have the squeaky brake problems others have mentioned as well. It's a little irritating driving a $40K truck that makes more noises than my 1995 GMC did!