Speaker Hum through Krell 400xi/Yamaha RX-V2700

Hello,

I thought I could figure this out on my own but I guess I was wrong. I have a large number of components which I shall list...

Transport
DAC
Krell Integrated Amp
Yamaha Receiver
DVD Player
HD Digital Box
Toshiba LCD

I have the Krell connected to the Yamaha RX-V2700 via the THR pass through option with L/R Pre-out on the Yamaha feeding the assigned slots on the Krell. All audio related power cables are connected to a Blue Circle conditioner. The television and DVD player are connected to another power bar (cheap Acoustic Research) The Television is connected to the Yamaha via a single HDMI connection. All other video equipment is connected to the Yamaha directly.

Whenever I switch to the THR input on the Krell to use the Yamaha for movies or television there is a faint buzzing sound from the speakers. I thought I could fix this problem by purchasing a ground level isolating transformer which basically separates the ground (The Krell has grounded plug, the Yamaha doesn't) but it didn't totally cancel out the noise. When no source is playing and the Yamaha and Krell are on I can hear a faint buzz which sometimes sounds as if its fading in and out. On two channel playback (S1 input on the Krell) the speakers are dead quiet; as soon as I switch back to S2 (THR by-pass input) that faint noise comes back which gets louder for the slightest second and fades back to its normal constant hum.

Questions:

Has anybody experienced this before?

How did you overcome it?