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sprinkles08, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 22292
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Bill, I have a 2006 Grand Prix that just started making an

Customer Question

Hi Bill, I have a 2006 Grand Prix that just started making an odd engine noise (sounds like its coming from behind the glove box). First I would have called it a whistle, now it's getting more metallic sounding. Only at 2500-3500 RPM and only when engaged in a gear (can't replicate in neutral.
Thought exhaust system at first, given that I can change the pitch with the rpm... now it happens in all gears (so not just a single gear tranny issue) and only at 2500 rpm... any ideas?
Submitted: 1 year ago.
Category: Pontiac
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to Justanswer!

Does it only make the noise when using a/c or defrost?

Customer: replied 1 year ago.
No, completely independent of a/c or blower, or heat.
Seems to get worse the longer the car is running.
Expert:  sprinkles08 replied 1 year ago.

Can you hear the noise from under the hood?

Customer: replied 1 year ago.
Hard to say - I can't replicate it in Park or Neutral, and I don't have a lift that would allow me to run the car in gear while looking under the hood.
It's definitely under the hood, somewhere central or slightly right of the center console, sounds closer to the firewall than to the headlights. Would the alternator be sensitive to RPM to that degree? I would think it would be noisy the whole time, not just at specific RPM?
Expert:  sprinkles08 replied 1 year ago.

It's possible that the alternator is making the noise.

Does the car have to be moving or will it make the noise if you brake torque it?

Customer: replied 1 year ago.
Ok, I did a little more experimenting. It was tricky but I got the sound to occur under brake torque. A little higher in the RPM range. I also managed to make it happen (very short duration) in Neutral/park when I rev really fast, it occurs at low RPM but only very fast as the RPM pass from 1000-1500 and only happens when I rev hard... no issue when I rev gradually in neutral.
It's starting to sound like a high pitched grinding sound. Not like a brake grind, but at first I thought of a bottle whistle (from inside the car) and with the windows down, driving by a wall or median, it's more metallic and like light grinding.
I will get someone to try and listen under the hood as I brake torque it to see if they can pinpoint the location. Let me know if anything sounds plausible. No performance deficits or issues, no shifting issues, no torque or acceleration issues, hesitations, or bad starts... I am puzzled. and it's pretty loud... noticeable at highway speeds from the car next to me.
Expert:  sprinkles08 replied 1 year ago.

Does it change at all when turning?

Customer: replied 1 year ago.
No. it's not a belt squeal or power steering sound.
the belts look good, not frayed. bearings are good. It is in direct response to the throttle being pressed. At 2500 rpm- 3500 it makes the noise when the accelerator is pressed, if I come off the gas, it goes away. Not related to anything else I can duplicate. Not AC, heater, steering, brakes?? happens in every gear (automatic, but it is not specifically at a certain speed, happens in 1, 2, 3 and so on. Even when the shifter is in 1, I can make it happen, and at highway speeds in*****
Can't get it to 2500 RPM in reverse, so I am not likely to try that one.
Expert:  sprinkles08 replied 1 year ago.

If it's related to engine RPM and will happen sitting still then it's not going to be anything to do with the heater, steering or brakes. It's something in the engine, trans, or an accessory.

Does it do it with the oil cap removed?