Grand Prix Hum Please help!


I have a 97 Pontiac Grand Prix GT and I live in Italy (military Spouse)! When i accelorate or step on accelerator even in nuetral or park there is a loud humming noise coming from under the hood. It i mainly coming from the serpentine belt area but it is not the belt slipping. It is getting louder everytime i drive. I have not really lost any power but a few times that i tried to start the car it took a few seconds to kick on. I know the air conditioning compressor is bad, but would that have anything to do with the humming noise. It sounds like either and electrical hum or a pump going out. It is starting to idle pretty rough as well. I am overseas and it is hard to find a mechanic. any suggestions?


i am assuming, without knowing your model car, but it sounds like your air pump is going.

from your description it also could be either the idler pulley, the alternator or water pump.

the humming noise could come from any of the above, however with the comment of the car running rough, that make me think first of the air pump. sorry i cant help find a mechanic in italy though. ask your other ‘family’ there where they go for mechanical work.

how many miles, which size engine, and what (mechanically has been done to the car in the past?


I would guess the bearings on one of the things the belt drives is going bad. It might be the A/C in fact that could be why the A/C is not working. It also could the the alternator or maybe an tensioner. In other words someone there will need to spot it.

One good trick is to get a length of garden hose about three feet long and use it like a stethoscope to find which part is making the noise. At least then you will know what part is going bad.

I suggest you don’t put it off too long as it may freeze up.


another thought when i read the other post by JEM.

does the hum happen when you have the AC on, or off?

is the hum different, or does it go away?

if you leave the AC off for a while see if it goes away. that would help eliminate the ac compressor as the fault. mind you it may still be the pulley of the AC compressor, but usually it will free wheel if the AC is off.


The noise is coming from the ac area mostly… when the ac is off. I am too afraid to turn it on… when i did before it ticked really bad… The engine is the 3800 series II 3.8 v6 I actually replace the previous engine with a junk yard engine with about 50k on it. The old engine the crankshaft snapped on. The only italian mechanic i found that spoke english said to bring it in and he would put a shorter belt on it to bypass the ac to see if that was the problem. if not then he would go from there. does that sound safe to you? when you say air pump…do you think there could be a vacuum leak as well?