Have a 1999 honda civic DX with 130K miles.
Had a transmission rebuild and full motor mount replacement about 2 months ago, and a radiator replacement 4 months ago. No other major issues.
Recently it started getting a rattle (sounds like shaking ball bearings in a tin can) when put in reverse or sometimes when stopped with the car still in drive. Does not happen when the car is driving forward.
When in the passenger seat it sounds like the rattle is coming from directly behind your head, the first few times I heard it I instinctually looked over my shoulder.
Had a friend sit in the car with it stopped in drive so I could look around the outside for it. He could hear it from inside the car but I could not hear it outside.

Need some help please.

 

dust shield or check that exhaust hangers keep exhaust from touching the car.

 

Put wheel chocks behind the tires, put in reverse and then look for the rattle.