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.
sounds like it could be something exhaust mount related maybe? that could be related to the change in rpms. It sounds like it only happens while the gas engine is running?
That's a great guess, Iris. I actually just had the cat replaced on that car, and the shop had a problem when trying to bolt on the cheapo aftermarket cat I was swapping in. The manifold flange was too thick, so they cut the one off the OEM cat and welded it to the new cat. Seemed good when I left and for a hundred miles or so afterwards, but maybe one of the bolts backed out. I'll check it out. thx.
Good thinking, Merkey. The aftermarket is a single cat, instead of the two OEMs, so there's a lot more room in there. And it has a deeper rattle than the thin sheet metal of the heatshield would make. The OEM cat had some of the heatshield attached to it, so it's gone. But I'll check that out. I haven't had time to mess with this car again.
