2002 Tahoe LT - Grinding noise

[johnhenry]

Hi guys, I just picked up this beautiful '02 LT - European version, runs smooth, but there's this maddening grinding sound that comes on and off randomly every time I start it - sometimes it comes on after I switch off the engine (like if I stop for fuel during a trip) almost always after I cold-start. It isn't the engine-RPM related though the sound is pretty constant for about a minute regardless of RPM speed, then after about 30-45 seconds it goes off and comes back on randomly

...any thoughts ? I'd be grateful for any ideas...

Thanks a lot.

 

[SteveCV]

Possible Autoride?

You didn't say, but if it is coming from the back and not the engine compartment, maybe it is your autoride compressor adjusting the height of the rear shocks? The back bumper should raise very slowly when the compressor is running. It will also run longer if you load up the back with people or cargo or hang a trailer off the back bumper. (I used to think it was an in-tank fuel pump when I first bought my '05)

 

[johnhenry]

Maybe

Thanks for that Steve, it actually seems to come from under the truck, which is kind of unusual, does the autoride grind ?

 

[SteveCV]

I don't know about grind, but it is very audible. Closest I can describe it is it sounds like a tiny jack-hammer. As I recall, without looking, the compressor is mounted on the frame by the rear axle. If you get out or put your head out the window it should sound like it is behind you. Or have someone else start the truck while you're back there.

I've grown to appreciate it over the years but it isn't exactly a "stealth" feature.

 

[johnhenry]

Wow thanks for that Steve, it's a very interesting thing, you are absolutely right, it does sound like it's coming from behind me, but when the engine is running it is very loud on the inside but almost inaudible on the outside... Do you know if there is a fix for this noise ? also how long is it usually before the bumper rises ?

 

[SteveCV]

I guess I don't know if your truck and mine are more noisy than others. Maybe somebody else will chime in. Oddly enough, for someone who normally asks about every little noise, I've never asked if this noise is "normal"... I've loaded my Tahoe with people and things and it seems to do what it is supposed to.

The bumper should rise almost imperceptibly as the pump runs. It occurs to me, if you want to prove it is the autoride, you can remove the fuse temporarily. I wouldn't leave it out, though. Some of these features are interrelated.