I am getting a very annoying grumbling sound at idle. Specifically, when I am at idle in drive with my foot on the brake. It is like a vacuum leak in the old days, but I don't think that is the case. It is worse, the more load placed on the engine like having the a/c on. The truck runs perfectly fine at all other times. It is only at idle like when stopped at a light. There are no codes stored in the computer. My throttle body is super clean. I recently replaced the spark plugs at about 95,000 miles. I just replaced the MAP sensor thinking that may be the problem. That did not solve the problem. Any help would be appreciated.

You know I am having the same problem right now for some reason. It happen a bit when in park, but gets worse when in gear and a/c on my envoy only has 83,000 miles I've changed the idle pulley the belt and tensioner fan clutch and still the same problem Im might have to take it to the dealer and have them tell me whats wrong can anybody help us out I would greatly appreciate it!

Another way to describe the sound is as if you have the steering wheel cranked all the way to one side where the p/s pump puts extra load on the engine. Since my post, I too have replaced the idler pulley and belt tensioner, and both O2 sensors. I have used my scanner to check fuel trim levels, and they are well within spec at +- 2%. There is really no change in the RPM while the engine is making that noise. I have also run the engine for a short time with no belt installed. When I put it in gear and hold the brake, the sound is gone. I believe the issue is not internal to the engine or a vacuum leak based on those tests. There are basically 3 more pulleys besides the crank. It's either the alternator, A/C, or power steering. A/C and p/s pulleys drive a compressor and a pump so I don't think there are bearing issues to deal with. I would like to try to replace the alternator pulley, but I need to find one. I will try the junkyard. I suspect it is the alternator pulley because I have had a similar problem in a volkswagen. The problem is that the pulley is not sold separately. Let me know if you have any luck with a dealer diagnosis. It's really starting to drive me nuts.