Ever since I bought my MX-6, there was a very slight rattling/clicking sound whenever I stepped on the gas. Not thinking it was anything serious, as well as having no money to fix anything that was wrong, I left it. But now that It's getting warmer out, the rattling is getting a lot louder, and when I idle it sounds like a diesel truck engine. The noise seems to be coming from the back of the engine itself. Any ideas what could be wrong? It's a '97 Auto with the I4 engine.