Can someone help me on this. i am trying to figure out what the culprit is for a rattle i am hearing from the engine compartment when i turn on my air conditioning in the car. i've been hearing it for a couple of weeks, and this weekend when i heard it, i popped my hood and it sounded like it may have been coming from the area near the alternator. if i turn the air off completely in the car, the rattle stops. if i turn it on, the rattle comes back.

any ideas what it could be? could it be the alternator making that noise? i thought the alternator was always running in order to charge the battery while you drive. could it be a pulley? is there a specific pulley that only turns when the air is switched on? again, the rattle goes away completely when i turn the air off, but comes back when the air is on....and it is definitely coming from the front left area of the engine bay, right about where the alternator is located. i have to turn the air off when i pull up to to stopllight because i am embarrassed to have my "luxury" TL rattling next to a toyota or chevy...any help would be appreciated!

 

ok, i may have found what it was. i found a thread on here called "tensioner pulley?" and in there it says that the idler pulley seems to rattle, so i am going to replace that and see if that solves the problem...i'll report back in a couple of weeks when i have the time to actually do this.