This should be a short list of possible problems. I don't hear well but a rattling noise coming from the front of the car. My guess about any car would be a bad pulley, maybe a tensioner pulley, or one on a pump or compressor. It doesn't rattle all the time, but seems to be associated with the decreasing/slack engine RPMs. Maybe the cooling fans have a bearing that goes out? I thought about a wheel bearing, but it does it when I first start the car, before backing out. I'll go look at it when it quits raining. Can a CV axle make a rattling noise? Can the AC clutch loose its bearing - sound doesn't seem to be associated with the AC being on or off. Does that idler pulley bearing go out a lot? Can't recall but one before, a long time ago.
