"Chattering" sound, almost like an auxiliary fan

[streetwaves]

Hey guys, I've noticed that sometimes after driving for a while, at a light I'll be idling and suddenly a strange chattering mechanical noise will start up, almost as if it's an aux. fan kicking on. I asked the mechanic that inspected my car before I bought it, and he said it was something to do with the fact that the A/C doesn't work, something about a certain component "spinning freely". Ring any bells? The car runs great, and I notice no difference in anything when the noise starts. It goes away usually after driving it and doesn't always come back.

[jlevie]

You could have a bad A/C compressor clutch that is rattling at idle, or if could be bad bearings in any of the other belt driven parts. you can easily tell if it is the compressor by removing the belt. if the problem goes away you've found the cause. If not remove the each of the other belts and rotate the pullies to check for bad bearings.