Midnight Ruby

Suddenly I have sound problems. Even if the Audio is off, there is a thump, thump, thump (at a rate of 40 per minute) non-stop! This started 4 days ago. Since then, if the thump is absent, I can turn on audio and get radio or cd just fine. But, it will quit and the rhythmic thump starts again. I think its worse than silence! I have an appointment at the dealer tomorrow morning. Any ideas on this problem? I don't want a big bill and no solution and I think I'm crazed from the constant thumping.