98 gst, Under Hood Grinding Noise

[cottonballs43]

I need help pin-pointing this noise. Its coming from the right side of the engine bay where all the belts are. Sounds like a bearing going bad.. like a grinding hum, I took the belts off so the alternator or water pump would not spin, the sound was still there. It happens as soon as you start the car and doesn't go away until you shut it off except for if the car goes under 900rpm then it magicly goes completly away. Under load the noise isent too bad, like I said just sounds like a bad bearing but sitting at idle if you rev the engine it gets very loud and raspy. I work at a shop, we all checked it out and have come up with nothing other than maybe a cam shaft bearing going bad (probeing with a stethoscope leads me to believe its not though), although I have tested the alternator and water pump I'm still not going to rule them out. The idler pully and tensioner pully don't seem to be what's making the noise when we probed it. I just dont want some pully to freeze up and heat my timing belt or anything like that. any advise would be great as well as questions. The car has about 140,000 miles on it, 5 speed trans, front wheel turbo, all the belts look fine.

 

[InvaderGSX]

Did you look underneath the lower timing belt cover? That happened to me once and I thought I had a bad bearing at it was a balance shaft belt that snapped and was in there so good it was rattling around. Another thing is a balance shaft is out of wack. You have to take your timing belt cover off. There's a lot of stuff down there that could be making that noise. Take it off and turn the car on and take a look. YOu have to remove the top and middle covers to get to the lower one which means you have to remove all of the pulleys like the crank pulley, water pump pulley's, and all the belts.

 

[theSicKness]

Me and my friend had the same problem with his car. after a couple of months of looking we finally tore the motor down and came up with the balance shafts, one of the balance bearings in the motor came unsteated and was grinding on the shaft its self. like you said it didnt make a noise under 1k but above it did. If you come up with nothing id take off your front case and pull the balance shafts and check.

Gl
Jesse