This is a 1999 Oldsmobile Eighty Eight LS.
When you start the car, you can hear, coming from the driver side under the hood, a weird rattling sound. It sounds like a metal ball being shaken in a metal can. It's not loud, but it's clearly audible. More specifically, it sounds like it's coming around the area where the EGR valve is, but I can't be sure. The sound does NOT go away if the car is warmed up or cooled down. It remains constant when the car is turned on, that's all. I was thinking a ball bearing or something?
Any idea what may be causing this? The car drives perfectly fine, there's no warnings or CEL.
Thanks!