Muse 160 question

I recently purchased a Muse 160 power amp. based on very good comments from audiophiles here and other audio sites. The comments on this amp. are spot on, great amplifier with very liquid mids and spot on images. The amp. also rocks when it needs to with good and very defined bass lines. Right now i'm using an OCM 55 preamp. in balanced configuration, even though i'm not sure the OCM is fully balanced. It doesn't matter, the system sounds wonderful and this is coming from a tube guy. I do have a question for anyone who owned this amplifier in the past and it has to do with a faint hum coming out of it. Is this a common thing with this amp. or is this a configuration issue with my system? I haven't tried to trouble shoot just yet hoping to get some input from previous owners. I definately appreciate your advice.