After trying many things and playing sub hum detective I finally found a solution - the Ebtech Hum Eliminator. I had given up for awhile but thought I'd try another search here and found this device mentioned. Initially I connected it between my receiver and parametric eq but that made the hum worse. I then moved it between the eq and the sub and presto! Levels or quality don't seem to be affected. Beck's Sea Change on SACD still rattles the walls.