I recently purchased a crown XLS 2002 and I can hear a slight hiss from the inside of the amp (supposedly a PSU hiss). It's >15kHz, so not too bothersome, yet in a dead silent room I can even hear it from two meters away from the unit. Does your crown hiss internally too? Is there anything I can do to make it truly silent (except for wrapping it in a blanket)? Most users complain about tweeter hiss when using those amps but I don't have that problem (using XLR connection).
Funny thing, I switched from a class AB amp with rumbling PSU to a class D amp with hissing PSU. It's a catch 22 situation.