Engine noise after timing belt replacement

I recently got my water pump and timing belt replaced on my 95 Hyundai Elentra. As soon as I drove out of the garage parking lot I noticed that the engine was considerably louder than it prior to the work being done. The sound got louder as the rpm's increased but when the car was idling was completely silent. It doesn't seem like an exhaust problem but more of an engine noise. It this because of incorrect tensioning of the timing belt, if not what could this be? Will the noise eventually subside when the belt stretches some (this is what the garage told me when I called them)? Should I take it back to the garage?