Owned an 03 G35 AT for about 3 weeks now. No problems other than bad tires (just replaced), and the usual bad hood hinge. Ran it through the automatic car wash last night and noted a belt-type whining at anything below about 1600 rpm. Abo 1600 to about 2000 rpm would get a bit of a whistle/squeal. Thought I got a belt wet so parked it last night and this morning started it up and it was better. Only wined/chirped at idle. Thought I would grab some belt dressing so swung by autoparts store and grabbed a can. Got home with it and no more whining/chirping. Well, I got this can of dressing and shouldn't hurt the belt anyway, so squirted some on both the main belt (the one to the fan) and on the one that drives the AC. No change in sound or anything. Shut it off, went inside for a few minutes, came out for a trip to the home depot and, OMG, squeeling/squalling noise at startup and idel. Got the can out again and first sprayed the AC belt, stopped immediately but began to chirp and whine again in a few seconds. Sprayed more on it and it quit at idle. I think, OK, that got it but i get in the car and drive and now it whines and squeals at anything but an idle. (exact opposite of this morning). Drove it about 15 miles, no real change, still the squeal or almost a whistle and whining going on at anything but idle. I turned on and off the ac, kicking in the compressor and it doesn't seem to make any difference. The tone or pitch of things doesn't seem to change, only whether or not the whine/squealing is there and the volume of it.

Belt dressing ain't going to dry out like water anytime soon. Should I suspect a bigger issue with a device? Can really see down in there what other devices this belt drives right now. I presume the tensioner is spring loaded and "automatic" so no manual adjustment there? Thoughts or suggestions welcome. BTW, it has 166K on it.

 

OK, I just went out and dropped the plastic cover, tightened up the pulley for the AC belt, squalling even at idle now. I'm guessing the belt or the pulley is bad. AC on or off, doesn't make any difference.

 

how old is the belt?
if the belt is old enough it will squeal.
or if it has wear on it, such as cracks and glazing.
if the by is new, it is possible your ac pulley is slightly slanted and it causes the squealing.

 

Turned out it was the tensioner pulley for the AC. Replaced it and while down there, put on 2 new belts.

Now going to install new spark plugs and hope for an MPG miracle.