I own the Pass X-250 and have no humming issues whatsoever and I have never heard of any issue with this amp either. The commenst above are correct regrading the sound of the Classe and Pass except that I do not find the Pass analytical sounding at all. I do notice that since I have been leaving all my components on, the sound is very natural sounding, with great deatails and dynamics. I also recently changed my ICs from AZ Sil Ref rca to XLR form the Pass X-1 to the X-250 so I do not know if this made a difference. The high frequencies are much better leaving the X-250 on all of the time, I would not have thought this but someone told me to try it and it has worked for me.
Happy Listening.
Happy Listening.