I have a 1996 Subaru Outback. There is a strange noise emanating from the center/front of the car. It only occurs when I stop accelerating over the speed of 50 mph. It sounds like a combination of a marble rolling around in a coffee can and a baby rattle. No sound at lower speeds or when I accelerate.
Any thoughts?
More than likely, you are hearing the sound of a loose or damaged heat shield on the exhaust system. When the heat shield is not in like-new condition, it will tend to vibrate harmonically at a specific RPM range.
Some cars with loose heat shields will have this problem at low speed, some at a specific RPM range at highway speed, and others will do it when the engine is idling. The reason for the variations noted above is that no two heat shields have been damaged in the exact same way.
Have the car put up on a lift and–if it is indeed a loose or damaged heat shield–the fix is a cheap one, namely using a screw clamp to secure it. However, only an indy mechanic is likely to agree to this low-cost solution. A dealership might actually want to replace part of your exhaust system–at a fairly high cost.
Another possibility is a disconnected/broken exhaust hanger. This would also be apparent when the car is put up on a lift.
If the noise is not from a loose heat shield or a disconnected/broken exhaust hanger, I suppose that there are other possibilities, but I’m not sure what they might be.
Second for VDCdriver on all points.
At one time many years ago there were some issues with heat shields and Subaru issued a service bulletin about the problem. Their cure was to drill a small hole and insert a small sheet metal screw until it bottomed out.
That sounds somewhat crude and a bit hokey but it’s a quick fix and works in most cases.