Grinding/ Rumble/ Vibration Coming from front of car along with power loss- '04 Grand Prix GTP

Car: 2004 Pontiac Grand Prix GTP
Engine: 3.8L Supercharged
Mileage: 94,300 miles

Usually after driving the car for a long period of time (approx 20 miles or more), Ill begin to hear a grinding coming from the front of the car. The grinding/ groaning can be felt in the gas pedal aswell. Depending how hard I hit the gas the frequency increases. Im not sure if this is associated with the grinding, but i noticed that when I turn sharply and go easy on the gas and progressively add pressure the car will cut out until i cut straighten the wheel. Then all the power I requested is applied all at once.

What the locals think:
CV Shafts- Sears told me the first time i went to get them checked that my CV shaft boot was a little loose, suggested changing it. Then I went back two weeks later and they denied saying that and said my cv shafts were fine. (talk about confusing)
Wheel Bearings- Someone I know said my wheel bearing could be slipping or my traction control could be on its way out, so i replaced both front bearings.
Tune up- Someone suggested it could be mis-firing, with it coming up on 100,000 miles, i did a tune up. (plugs, wires, coil packs)
Transmission- Someone said the transmission could be going bad. So i did a flush and inspected the fluid, no shavings or any sign of extreme wear. (car shifts great too.)
Clogged Catalytic converter- the cat was clogged, two new 02 sensors and a new cat didn’t even help with the issue im describing, but it does have more power now (:
Throttle Body- Someone said it could be a dirty throttle body…so i had that cleaned also.
and finally, some electric temperature sensor- someone said it wasn’t getting the right fuel mixture, so i replaced the $30.00 sensor to remedy that.

Fuel pressure was also tested to ensure the fuel pump was doing its job, everything checked out great.*
My attempts have only costed me tons of money and no answers. Can someone please help me!?

Side note: it’s just like this entry I found about a 2004 trailblazer except theres a couple differences, they have an engine light on, and I dont and they dont have any power loss. So this hints that maybe what im experiencing is a mix of two problems??

Similar issue with trailblazer:
“This just started about 1-2 weeks ago. My Trailblazer is making a growling/grinding when I accelerate from a standstill. The noise is coming from under the vehicle in the front. It’s definitely gotten louder the past couple of days and only does it when I first start to accelerate; after the car shifts into 2nd or as I gain speed the noise stops. It doesn’t seem to be driving funny, no loss of power, just the grinding/growling noise and a sound like something is shaking/vibrating. Also, my service engine light just came on. Anybody have any ideas?”

The combination of grinding/vibration and loss of power makes me wonder if there’s something wrong with the supercharger. Has that been checked?

I have not had the supercharger examined, just out of curiosity are you hinting that my tension pulley could need some inspection? I do recall back when I first bought the car a year ago I brought it to a shop in southern Maine (I live in northern Maine) and they said I might wanna look into another pulley, but when I brought it up here everyone was saying it was fine. Would that cause the loss in power when i turn?

Honestly, I have no experience with superchargers. But I know they’re rotary compressors, and rotary things can develop bad bearings, etc, and make grinding/vibrating noises. And since you’ve checked many other things but not the supercharger, it might be worth taking a peek at.

One important fact you didn’t mention: does the car have to be moving for the noise to occur?

As for the power loss when you turn, that could be a separate problem. Are you sure the ignition is not cutting out? In which case it could be as simple as a bad ignition switch in the steering column.

Have you checked to see if there’s any oil in the supercharger?


Regarding the odd behavior when turning: if your car has power steering (i.e a power steering pump), it probably designed to bump the idle up a bit during turns. With my Corolla anyway, the way it works is there is a vacuum switch in the power steering pump, and during turns this opens up, and allows extra air into the intake manifold, which increases the idle speed. If there was something wrong with all that, it could cause drivability problems only manifesting during turns.

Did you ask your mechanic if it is possible to put your car on a lift, and run it at various speeds there, letting the drive wheels rotate? On some cars this isn’t recommended, but if it is allowed on yours, might could get some idea where the noise is coming from. To me it sounds like a problem somewhere from the transmission to the wheel. Where though? That’s the question.

Maybe do an experiment where you idle at various rpms, drive at the same rpms, vs coasting at the same speed, note the differences in the sound, could provide a clue. Best of luck.

I have not checked the supercharger, will make a note of it and bring it up to my mechanic. Also, the issue when turning; my strut mounts are HORRIBLE. There’s a real hard binding. If the power steering pump needs to bump up the idle and there is too much pressure on the suspension, would it make it more difficult to follow through with that?

Yes, The car must be moving for me to experience the power loss. Usually it occurs when accelerating from a stop sign and turning. (I must be turning for the issue to occur). Also, I can recreate the issue when not turning, that is a little more difficult and doesn’t usually happen alot. But if im going steady at 50mph and I slam on my breaks because I missed a driveway and I come to a complete stop and then immediately get right back on the gas, it will rev and not move. It will stay stationary for about a second and then all that power from revving gets distributed all at once resulting in a really powerful take off (often resulting in squealing of the tires).

Another helpful fact is that the car turns fine when im stationary (backing out of a parking space and turning—low speed.). I can turn my wheel until the cows come home while the car is still and it doesn’t skip a beat.

As much as I would like to add full coverage on this car and give it some amazingly painful death, I need it to last me another 5 years or so.


“please don’t post your personal phone number or email address in your questions.” This is a direct cut and paste from the “discussion rules”

This is for your own protection

We can send private messages to each other. By clicking on a username, you will get the option of sending a message to that individual.

I do it from time to time. I feel it works pretty well.

If the struts are bad, it is possible the extra travel in the suspension is rubbing the insulation off of important wires. Worn engine mounts with too much give can cause this kind of symptom too. Maybe get a flashlight and look in the car’s nether regions for wire bundles that look frayed. This extra movement can also adversely affect mechanical linkages, like for the throttle and transmission.

@db4690, My bad, I honestly didn’t even look at the FAQs. Nor did I know there was a messaging system developed.

@GeorgeSanJose: Will have my mechanic inspect all wiring and engine mounts when he inspects the other suggests. Thank you soooo much!

lots of info on grand prix websites. the kids like to mod the super charged cars. the supercharger has a plastic bearing coupler that gets noisy. not real hard to change out and not expensive. folks talk about changing the supercharger lube oil. none seems to do it. like changing brake fluid. dont know if new and old fluid has ANY affect on noise issues or what the deal is. the boost valve is controlled by engine vacuum. sometimes the vac hose blows off. they call that a blower sneeze. than the supercharger will make no boost. happened to my kids car. he was not happy with no boost. plug hose back in.

TJ … since you don’t have problems with the idle when turning the steering wheel when the car is stopped and idling, my idea about the power steering pump vacuum switch for bumping the idle speed isn’t likely the cause. Best of luck in getting to the bottom of this.