I just installed a new ht system and have been noticing that in surround mode (any mode except stereo), there is a soft, high-pitched tone that emanates from all five of my speakers at volumes greater than -10db (the whine becomes more noticeable at high volumes). I have tried unplugging all of the components and the whine still exists. It seems to be coming from the A/V receiver itself through the speakers. Here's my setup: NAD T752 through MB Quart speakers (1030s, 330 and 530s). Anyone have any thoughts on this?