I just bought an 02' Impreza WRX Wagon and I'm hearing a noise that I am having a hard time describing when I let off the gas. When I shift and accelerate everything is fine, but when I take my foot off the gas there is a a rattling kind of noise. It's not grinding but it has gotten louder in the last couple days. Sorry for the poor description but as you can see I'm no mechanic! Any ideas as to what this may be will be appreciated. Thanks a lot.