Strange Noise

I recently (November 9, 2005) bought a 2001 Subaru Outback, 4 cyl, automatic. It has 110,000 miles on it, which is a lot. Here is the problem: whenever I drive it nowadyas, it sounds like there is a shroud or something rattling. It only gets louder when I accelerate. The car runs fine, just sounds like hell. Anybody know a reason for this 'rattling'?

It's the heat shield on the exhaust, get her up on some ramps and look at the heat shield on the exhaust around the gearbox area, the welds tend to break in that area.