I have an annoying rattle in my 03 Legacy wagon that started a couple months ago. It is definitely coming from the front half of the car. It was small at first, and wasn't constant.  Now, it has grown to a constant loud rattle at idle.  When I accelerate, it rattles louder and faster upon initial accel, then goes away once underway. I have checked all the shields, and none seem to be loose.  The only thing I can think of is the cat.  Agree, or other ideas of what it could be?

Edited May 20, 201510 yr by Timberwolf530

Never had a cat rattle but the heat shields are notorious.

if you crawl under there and smack the cat with your hand can you hear stuff inside rattling freely? if so the cat has broken apart internally and will need new one.

Edited May 20, 201510 yr by sirtokesalot

When an exhaust shroud comes loose it makes a high pitch zzzzzzzzzzzzing, and clatter sound. Broken cat media sounds like gravel stones bouncing around in a metal bucket. Most likely it is a loose shroud. Can be quieted down with a hose clamp, or use a hammer and drive in a large bolt as a wedge between the pipe and the shroud to prevent it from rattling.

A constant rattle is good because you can easily crawl under the car and listen for the source. A stethoscope is good for reaching further under. Jack stands will let you get all the way under.

stainless steel hose clamp and you're done