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Knocking/rattling sound at idle.

D

dvernst

Well-Known Member
After my car warms up when it is idling it's making a knocking sound that I can't pinpoint. I took the belt off, and it seemed to go away, but not sure what pulley might be bad. The tensioner pulley bearing seems fine. Do you think it could be the ac clutch? It doesnt make noise when I spin it, but it does have some back and forth play. The thing that's weird though is that when it is making the noise it sounds like it's from inside the motor. It doesn't sound like it's from the belt area. Any one ever experience anything like this? Thanks. Dave
 
I've had it where the tensioner clicks/knocks from the pivot point where the spring is, only had it happen once but something to check. Remember noise can travel through solid objects and throw you off, but you should be able to pinpoint the noise while running using either a long screwdriver/prybay or a leangth of heater hose to listen to specific points.

HTH,
Steve
 
dvernst said:
After my car warms up when it is idling it's making a knocking sound that I can't pinpoint. I took the belt off, and it seemed to go away, but not sure what pulley might be bad. The tensioner pulley bearing seems fine. Do you think it could be the ac clutch? It doesnt make noise when I spin it, but it does have some back and forth play. The thing that's weird though is that when it is making the noise it sounds like it's from inside the motor. It doesn't sound like it's from the belt area. Any one ever experience anything like this? Thanks. Dave
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I had the same problem and it turned out to be the alternator.
 
Wasn't there two different belt lengths suggested for this car? I think I remember at one time one of them was too short and caused the tensioner to hit something. Sorry I don't remember the details off hand but I know that Steve will be able to add some information on it.

As Steve suggested, use a long screwdriver or something solid to check and listen to different areas to pinpoint the sound.
 
Try a new belt before you start replacing parts unless you can pinpoint the problem. Like Jared said, if there is a belt that is "ok" when new it will stretch and can cause knocking.

Jason
 
Yeah I just picked up a stethoscope from Auto Zone. Goin out to the garage now. Yeah I only checked the bearing on the pulley with no tension. Thanks...
 
Well it definitely goes away when i take the belt off. I tried taking tension off while it was running, but the noise stayed. I can hear it from underneath the car too. i can hear a little noise in the a/c pulley, but not like the sound im looking for. Hopefully it's not a crank bearing, or something like that...
 
tensioner pulley tapping the A/C pulley? Happened to me when the belt dried out and probably streched out as well.

Check the ring around the crank pulley as well. Maybe its tapping the crank sensor?
 
dvernst said:
Well it definitely goes away when i take the belt off. I tried taking tension off while it was running, but the noise stayed. I can hear it from underneath the car too. i can hear a little noise in the a/c pulley, but not like the sound im looking for. Hopefully it's not a crank bearing, or something like that...
Click to expand...

wouldn't be a crank bearing if it stops when you take the belt off. I would go buy a new belt if you haven't replaced it recently, cost like $20 and it's good insurance. Could explain why it makes the noise with the belt and not without it.
 
What about a worn thrust bearing? Taking the belt off kind of unloads the thrust at idle,does it not?

But then again...I'm very pessamistic about engine noise.

I hope it's just the A/C clutch or something easy.


...
 
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I have that problem too. My tensioner is hitting the A/C clutch pulley. just noticed that tonight while I was replacing the alternator. Easiest way to tell was the groove in the clutch pulley from the tensioner hitting it.
 
WS6 said:
What about a worn thrust bearing? Taking the belt off kind of unloads the thrust at idle,does it not?...
Click to expand...

Taking the belt off does unload the thrust bearing.

Does it make the noise in neutral with the belt on? Check that if a new belt doesn't fix it.

Get the belt I suggested and run with it.
 
Yes it makes the noise in neutral. The noise is the worst when it's idling, and the rpm's fluctuate a little bit. I can get it to rattle by moving the tps down with my finger. There's a split second when the rpm's drop, and that's when it makes the noise.... There is plenty of clearance between the two pulleys. It almost looks like it might have a shorter than stock belt on it already. I have to bring the tensioner all the way back to barely slip the belt off..
 
With the belt that's on mine now if it were any shorter it would hit the bracket also. I thought my bracket was modified though because I have a different intercooler. The belt is prob. 2mm from the bracket now...
 
Nick Wise said:
I tried this belt from Napa And it is actually too short. Same part number but the dimensions are 20mmX1598. the problem is it rubs on the intercooler bracket between the tensioner and the alternator. Any help on this?
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Hmm I didn't have that issue. Lemme look into and see if I can see anything.

Jason
 
dvernst said:
After my car warms up when it is idling it's making a knocking sound that I can't pinpoint. I took the belt off, and it seemed to go away, but not sure what pulley might be bad. The tensioner pulley bearing seems fine. Do you think it could be the ac clutch? It doesnt make noise when I spin it, but it does have some back and forth play. The thing that's weird though is that when it is making the noise it sounds like it's from inside the motor. It doesn't sound like it's from the belt area. Any one ever experience anything like this? Thanks. Dave
Click to expand...
Dave - did you ever get this problem resolved? I think I have the same issue.
 
No, but I haven't really spent anymore time on it since this post. Let me know ifyou figure anything out. Thanks.
 
How did you figure out it was the alternator? I think it is either the tensioner, the alternator or the AC compressor, but I don't want to just throw parts at it.
 
We tried using a stethascope, but couldn't tell where the noise was originating from. I did the tensioner first because it wasn't too expensive. I was hoping it was the alternator because I figured the compressor would be expensive.
 
Ok. I finally figured out what it was. When I pulled, or pushed on the alternator the noise went away. Took the belt off, and when I would pull on the alternator it would move a little and stay. Started taking things apart, and I finally saw it. The 3 bolts that hold the bracket for ac, ps pump, and alternator to the motor were almost all of the way out. Had to loosen the compressor to reach one of them. As far as I know that bracket had never been removed before. Quiet as can be now. Thanks. Dave
 
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