This may be the same problem that I have mentioned several times and have never been able to solve.
In my case it happens with all Rt's (not just real drums) and it is "blip" that happens at the end of a song when the last bar ends. It sounds like an electronic switch off.
I have tried muting everything before the end but this doesn't help.
Tech support haven't been able to solve it for me either..
Some people say they hear it but it is very quiet. In my case it is quite loud.
Tony