I have a 2006 Silverado 1500 with that godawful 4.3 in it. It's got about 170,000 on it right now. Recently, I noticed a high pitched whine at idle and low speed that disappears under acceleration. It is not belt squeal. It almost sounds like some sort of air leak, think of an air mattress with a pinhole in it. I can't seem to find the cause of this obnoxious noise and I have no idea when it started because I usually have the radio on. If it matters, I just pulled the intake a few weeks ago to replace a bad injector. At that time, and since then, there are no apparent leaks related to all that.

Any ideas??

 

Nobody? Cool...