ROTEL RB1072 POWER AMPLIFIER EN FRANCE

Please read carefully: This amp is in excellent aesthetic condition and is fully functional. However an audible buzz can be heard through my speakers when this amp is switched on. It is most noticable at low volume. At higher volume, it sounds fine to me. Possibly I've not connected it correctly or the buzz is coming from another source.  The protection light goes on and off correctly. I know nothing about electronics so I haven't removed the cover. The Rotel is in excellent condition with no visible damage. It has always been very well cared for and has performed perfectly until recently. I have bought a RB1092, so I no longer need this RB1072.