I found mine is very sensitive to any noise in the signal chain; I mean, I know how a compressor works and it is certainly way better than the TC Electronic one it replaced, but I was using more gain owing to a change in preamp pedal (it only has ‘cut’ eq, no boost) and over 12 o’clock on the Keeley gain it really magnified a *very* slight hiss.
Took me ages to figure out what it was, too 🙄