engine compartment noise

[gotitmade]

2003 Tahoe. I've maintained it since new myself. I have an engine compartment noise which sounds like a ratcheting sound. It occurs at about 2500 rpm. Above and below 2500 it does not appear. Very noticeable when engine is cold. Seems to go away when the engine is hot. Sound occurs both at idling and when moving and its quite loud. Check engine light is NOT ON. I do not think it is an engine problem, but something associated with an attached engine component. Possibly the clutch fan. It does not sound like a bearing noise. When I was young, we used to attach a piece of thin cardboard with a clothes pin to our bicycles, so that the cardboard was between the spokes. When the bike moved it sounded like a ratchet, although as kids we thought it sounded like a motorcycle. That’s the best description of the noise. At this point, I have not gone far enough to isolate it. If you have any idea of what that might be please comment on it.

 

[gotitmade]

OK folks. I received no replys, but I did resolve the problem. The noise came from the AC compressor belt tensioner, which I replaced. But that is not the source of the problem. The AC compressor develops a slugging problem which will cause Belt Tensioner and Belt failure. And eventually the AC compressor itself fails.
GM put out a technicla bulletin: GM TSB# o3-01-38-019A

Look for my next post on AC compressor Deslugger Kit