I have just acquired a secondhand evo 4 and it seemed to be fine for a couple of days. I leave it powered up, but it started humming quite loudly this morning when it had no signal going into it. I turned it off and on again and it has not happened again. I have noticed there is a low level hum from it all of the time (I assume its the transformer), is this normal or should it run silently? It seems to be warm (not hot) all of the time and does not get much hotter even when playing loud. How warm should it be when not being used? I am concerned about the loud hum this morning and would like to know if anyone has any suggestions about what may have caused it. The seller did say he would take it back within 7 days if there are any faults. I am obviously tempted to try and get him to honour this promise. Any suggestions would be appreciated.