Does the hum come and go or is it constant?
My 7500 had a hum that would come and go constantly and I bought a Channel Islands Audio XDC-2 AC filter and it completely stopped the hum.
Apparently my problem was with standing DC on the line for some reason.
I didn't have this problem for the first few months and I don't know what changed but this little unit took care of the problem.
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Epson 3500 3D projector
93" Carl's Place Flexiwhite DIY screen
Outlaw 976 Pre/Pro
Outlaw 7500 for LCR & L/R surrounds
1- Emotiva Mini X-A100 for rear surrounds
2- Outlaw LFM-1 EX subs
Oppo BDP-105 Blu-ray/DVD/SACD player
Outlaw LCR (Snell Labs) for center channel duty
Tekton Lore monitors L/R
4- Emotiva ERD-1s surround speakers
Monster HTS3600MKII power center