I've come here asking for some assistance with an issue I am having with my 99 mustang GT. Sorry for my ignorance I am not really knowledgable when it comes to fixing cars. I'm trying to change that though, im tired of paying others to fix my car, I want to learn this for myself now. Anyways... After making a long drive today I noticed a rattle coming from under the hood. Working with a relative of mine we think we pinned the problem down to either being the A/C clutch or compressor. The reason I say this is because when I would start the car the rattling sound would appear. I would then turn on the A/C which would then limit the rattling sound. But now the rattling occurs regardless if the A/C is on/off. I can hear it more prominent now when I am idling at a light now. We haven't tried to removing the serpentine belt due to lack of time and tools. I am going to try and fix this this weekend. My question is does this sound like an A/C clutch problem or a compressor problem? I don't want to buy and replace the A/C clutch, only to have the problem actually be the compressor. Also is the vehicle safe to drive in this condition or will I screw things up more if I continue to drive it? All help is appreciated, thanks!