After reading the other responses, I suspect the noise has nothing to do with the class D amps but is more likely coming from a noisy preamp section. Since you've had 2 different units that sound the same and someone else also has a noisy unit, it appears some hiss is just inherent to this model.
(I looked at the specs and they are a bit odd - Peachtree states the S/N ratio is 96 dB but then claims a dynamic range of 121 dB. Strange.)
(I looked at the specs and they are a bit odd - Peachtree states the S/N ratio is 96 dB but then claims a dynamic range of 121 dB. Strange.)