Theos91LS

Greetings everyone,

I really appreciate this website. The subject at hand is a 1991 LS 400 with 100-120K miles on it.

After the engine is turned on, it begins to make an intermittent noise, that sounds like rattle or vibration. It reminds of the sound that those portable house box fans make when getting old, but louder. The noise lasts about a second, and then silence for a second, and repeat.
The noise sounds to be coming from the near the accessory belt.

After some warm up time, the noise gets quieter, but will occasionally make a loud one.

The noise will stop prior to warm up, if the AC is turned on. I see that one of the pulleys on the belt speeds up in spinning and the noise stops.

I've read a lot on here about tensioner and idler pulleys wearing out.

I'm thinking to remove the belt and spin the pulleys, listen for broken bearings and feel for any oscillation/wiggle.

Has anyone else had this problem? Thank you all in advance.

mattylex77

Sounds like motor mounts are bad

YoshiMan

I would check the individual pulleys with the belt off like you said. the freewheel pulley on the A/C might be going south, and activating the clutch might temporarily tighten it up enough to make it go away.

I had a similar problem with my 91' Camry V6. Whenever I turned the AC on, the car would screech like a banshee. I couldn't see it just by looking at it, but it Turns out the crank pulley had separated, and the drag from the A/C was enough to cause it to spin slower and grind against the inner part of the pulley.