Vibrating or "grinding" sound?

Question

I have a 2000 Chevy Z71. When I crank it up during cold weather, you can hear an almost "sewing machine" sound coming from underneath the truck. The dealer and I first thought is was a noisy fuel pump and changed it. The noise is still there. The sound travels along the underside of the truck, making it hard to pin point. It does not get louder during acceleration and eventually stops after about an hour or so. No noise during warmer weather.

Answer 1

The flywheel will sometimes make this sound in cold weather, but that is usually on a standard transmission.

Answer 2

It may be the power steering pump. To test simply take the serpentine belt off start it when the motor's stone cold and listen for noise. Power steering pumps often start to make all kind of rackets while warming up. This is a message that it may be time for a new one. I doubt that the pump's the problem because GM pumps are usually trouble free.

Answer 3

The sewing machine sound you described sounds to me like you injectors firing which is normal. Perhaps there is a little more clearance in them in the colder weather making it more noticable. My Nissan does the same thing and I put those in brand new. Its the nature of the beast

Answer 4

Hi,
There is a flywheel in the automatic transmission as well. I had a 1993 chevy that had the same problem , it kept going through flywheels, but that was not the problem, it was a bent camshaft.

Answer 5

remove the belt on the engine and see if the noise stops.(but dont let it run long enough to overheat)my guess is the smog pump.hard to tell without being there.But if the noise stops with the belt completly off you know its one of the parts it runs good luck

Answer 6

Vibration or grinding noise are mainly due to excessive wear of driving parts, or some times even due to misalignment of parts.