I have a 2002 GMC Envoy that has developed a shrill whistle. It starts after the car hits about 20 mph, stops when braking or at a standstill, and sometimes doesn’t start right away if the car is cold. My mechanic has checked things out and can’t find anything. He pinpointed the sound to the front right side, but replaced the wheel bearing and that didn’t fix the problem. Any ideas?
First you have to determine if this is caused simply b/c the car is moving, or if it is caused b/c the engine is at a certain rpm, or if the xmission is in a certain gear. Suggest you do some experiments to find out. The fact that it stops while braking may mean it is related to the engine rpm, not the wheel speed. You mention it goes away at standstill. But what happens if you increase the idle speed while at standstill? Does the sound return? Does it go away immediately after shifting gears?
Usually a wheel bearing problem isn’t a shrill whistle. More like a grinding our growling noise at higher speeds. At lower speeds, it is often worse when turning. Often makes a hrumpp … hrumpp … sort of sound at low speed, esp when turning. So it’s not surprising replacing the wheel bearning didn’t help.
My guess is it is some kind of air leak or a worn or loose belt. It is the engine in other words. Whistling is not uncommon with a valve cover gasket leak. Check to make sure the valve cover bolts are tightened to the recommended torque and tightened in the order recommended. If that doesn’t fix it, or change the sound, then you’ll need to go on a vacuum leak investigation. You’ll need to test every vacuum controlled device one by one for a leak. There’s an off-chance this is related to the pcv valve, so checking that out is worthwhile – even it is unlikely to be the cause – as doing so is usually easy.
Thanks - this is helpful! So I did a few tests and the whistle is there but very faint, when in park and revving the engine up to 2 or 3 rpms. It is also not there until the car hits at least 2nd gear. And it does not stop when braking, unless the car is close to stopping. Does that help any more?
Sometimes a stuck brake caliper can cause a whistling/screatching sound while the car is moving. But since you can hear it while the car is parked, unless there are two sources of whistling, the cause I guess remains a mystery.
Years ago I had an ancient volvo that would whistle at certain speeds. After driving me near crazy, I found that its aftermarket roof rack was missing an end plug and the air speed would play that pipe like a pan flute.