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GMC Sierra whistle

I’m having what I believe to be a minor issue w/my 2008 GMC Sierra (107,000 mi) it whistles when accelerating while the outside temperatures are cold. I noticed it toward the end of last winter, it never happened all summer, now that it’s cold again it’s back. It’s annoying, I checked w/the dealer they said it never happened. I figured they didn’t know. I was reading some blogs there were a lot of folks w/the same problem but no solid solution.
I read possibilities such as; Fan Clutch, Lower intake gasket, Air Filter housing, PCV Valve, Alternator, Power steering pump along w/several other guesses. Do you have any Ideas.

I believe an 08 (with the exception of maybe the 4.3 v6, I’m not certain) will have an electric fan, so if that’s the case, the fan clutch can be ruled out.

Any of the belt driven accessories could be the problem (alternator, water pump, any idler bearings), so you could remove the serpentine belt and check for any lateral play in any of the pulleys. While doing that, you might go ahead and replace the belt if that’s never been done.

One other thing to check is the air intake. Make sure all connections are tight. I’d recommend cleaning the throttle body as well, since carbon can build up inside, and I suppose could lend to a whistling sound during light acceleration.

I’m not certain an 08 will have a PCV valve either. My 05 does not have one, but has a “fixed orifice” on the valve cover that serves as a PCV.

Sometimes you can locate the source of a noise with a piece of heater hose. You hold one end to your ear and scan around the running engine with the other end of the hose while someone else makes the engine whistle.

Thanks for the suggestions, I’ll give them a shot.