I hope you can help me, as I am stumped. I've searched everywhere on the 'net to no avail. I have a Yamaha RX-V795a AVR. While doing a phase test for the first time in a few years, I noticed the rear surrounds in my 5.1 setup act differently than the mains do during their test. While playing the 'noise' for testing 'in phase' I can hear the 'noise'. While playing the 'noise' for testing 'out of phase' there is silence. I'm testing with the old Avia disc. Is this normal?