I just purchased 2 M-Blocks to go with my 755. Both M-blocks have considerable hiss even with the preamp (Denon 3803) mutted and even with it disconnected from the amp input, while all 5 channels of the 255 are dead quiet. Are your 200's noisier than the 755 or are mine defective?? The hiss can be heard up to about a foot away from the speaker depending on ambient noise.