Rattle Under Car

[Unregistered]

There seems to be a rattle from under the car that is there all the time, but most note able at idle and take off. The noise seems to be getting worse, it sounds like a can of marbles, dull not sharp like metal grinding. The MPG have only dropped 4-5 MPG over the life of the car, I get about 25-27 MPG highway and 20-23 MPG in the City. I have not been under the car to check but I was thinking it might be a loose heat shield or exhaust hardware. If this were internal to the engine I would think by now the engine would have died. Would get worse gas mileage with a bad catalytic converter? Is there a way to test the Cat to find out if it is bad? Thanks in advance for the help.

Thank You
John W. List
1995 525iA
298,000 Original Miles

[TimGinCentralNJ]

Hey John-

My first guess would be either heat shield, or your catalytic converter's guts have come loose (a common thing with age) and are now rattling around. Can't think of much else down there which would make the sound you've described.

Might be worth having someone you trust tap the pedal while your car is running, so you can take a peek under there while it's occurring.

Rgds,
Tim