A New Noise And Source

I took our new to us 1999 Bounder 34 out for a drive a few days ago. A new noise developed in a fairly short order. Almost, but not every time, I stop and then press down on the accelerator there is a "clunk" sound that appears to be coming from under the coach and sounds like it is very near the drivers seat. It only happens when either at a complete stop or at almost a complete stop and the transmission is in the lowest gear. It happens more than it doesn't, but sometimes it does not. I don't hear the noise at any other time. This just started, it was not there when we purchased the coach a week ago and drove it home. Anyone have a thought as to what I might look for or anyone had this same issue? Thanks. Chuck