loud noise under car when accelerating.

What is your question?

When I start the car and accelerate I have a loud noise from underneath close to the driver side. When I let off the gas pedal it goes down. The RPM's will go up to around 2k. When I put it in reverse it sometimes sounds like the car will die but never does. I looked underneath and the muffler looks ok but I'm not sure what else it could be.