Airplane Noise

[KimiFan]

My car has been making this noise that sounds like a airplane when it flys over your house. It kinda sounds like something is like rattling plastic or something. The car drives fine and it only does this when it is ideling or just really low RPM. What could it be, it is really loud and sounds horrible. Is this something i should be worried about and has anybody else heard or have dealth with this problem before. Also it sounds like it is coming from the right side of the car, towards the front.

[cali-ti]

so it does it when the car is just sitting or does it have to be moving? if it does it when sitting, i would pop the hood and see if you can isolate where it's coming from, at least generalize the area. something with the fan possibly?

[DeadpaN]

or the heat-shield

[Avus /5]

Or the cat. When the honeycomb inside my cat broke, it rattled like crazy at idle and low RPM, but I never noticed it at speed. Not sure if that was because of engine noise or because the pressure inside the cat pinned the loose ceramic in place.