Noise from Auto Tensioner

[jsudaria]

My 2003 M45 has been making some noise coming from the belt and pulley area. I have an upper auto tensioner and a lower one. The serpentine belt goes around the upper tensioner pulley and the pulleys for the AC compressor, water pump and alternator. The lower belt is the power steering belt. When at idle and/or begin to accelerate, I hear a whinning sound but the noise will go away when I turn off the AC. Since the noise is definitely coming from the pulley area I would assume it's the upper tensioner and serpentine belt since it goes away when I turn off the AC. I took it to a shop today and they claim it's the lower tensioner and belt (power steering belt.) Any thoughts??

Thanks,
Jason.

[The00Dustin]

If it goes away when you turn off the AC, why do you suspect a tensioner? I would suspect the compressor. If it could be the tensioner, it could also be the water pump or alternator They all have bearings. That doesn't help narrow it down for you, but your options are figure it out yourself, trust the shop, or plan on throwing money at it until it's fixed. The figure it out yourself option makes me nervous, it involves using an automotive stethoscope (or a makeshift alternative for one [for instance, a 2x2 or thick stick of wood]) in order to determine where the sound is coming from. Incidentally, if you do that, you might check everything, especially in case the lower tensioner is also making a quieter noise that simply isn't catching your attention yet.

[EdBwoy]

I want to throw yet another possibility - the idler pulley to the a/c belt system.
For a quick diagnosis, if you can, remove the belt and spin those pulleys by hand in a quiet area or use a stethoscope. If it's bad enough, you will hear and/or see the suspect pulley slowing down or with jerky movement.
Worse case, it's the a/c compressor bearing.

[jsudaria]

I had the upper auto tensioner replaced and everything is fine now. The reason I suspected the upper one, is because when I would turn off the AC the noise would go away. So you ask, why does the noise go away when the AC is off: the reason is because there is additional load on the engine with the AC on causing more of a chance of a vibration and making the auto tensioner work harder and eventually failing under the extra load until the AC is turned off, releasing the extra load.