I have a pair of Vincent sp-t800 monoblocks and one started clipping at higher volume, I get an occasional pop from the woofer. I have swapped speakers, speaker cables and channels to eliminate my preamp and interconnect's. The woofer does something unusual as well, it will pulse in and out like a sign wave as well. Lower volumes are fine. Has anyone seen this or what may be going in the power section to cause this?