What does bad compression sound like?
 

As above, what sounds does a rotary with poor compression on a rotor make?

usually no sound at all on the face with bad/broke seals. there's no real description of the sound. if u spin one on the starter with plugs removed, u can immediately tell a difference in the pressure of the air coming out of the plug hole on a rotor that differs in compression between faces.

Like money leaving your wallet. :)

On a serious note it is pretty obvious as mentioned with the plugs removed. By a $20.00 compression tester and find out for sure.

can u buy any compression tester
... and where do u find this compression tester

Many parts places like Napa will have compression testers, that is a great tool to add to your tool box. You don't have to buy the most expensive one either.

u can use piston engine compression testers. u just need to either remove the schreider valve or hold it in when doing the test. u don't want it holding the compression, it needs to release it. that's the only way to measure the compression on each rotor face.

LOL...like money leaving your wallet...that was a pretty good description. ;)

On a serious note, I split 2 apex seals out of my rear housing back in spring of '09. It ran on 1 rotor, but vacuum was all over the place (fluttering around 15in Hg) and it had absolutely no power whatsoever, obviously. Trust me, you'll know if you blew a seal that affects compression. :P

my exhaust makes popping noises by it self on a steady idle.
hmm, i can say its like a popcorn popping noise.