Foster_9 Did you check the voltage with an meter that reads RMS? If you know what that means then I don't have to say anything more, if not, RMS is the true voltage. Most inexpensive meters measure only an approximation of that. Rather than reading absolute value of the voltage the best thing to do is to measure the drop between the input to box and receptacle. Measure it with the system playing. If your system is off there won't be a drop, Ohms law and all that. Or measure it at the receptacle with the system unplugged and again with the system cranking. Of course taking those measurements should only be done by someone with some knowledge. There is risk if it is done wrong.
BTW I think the idea of switching the breakers on and off is a good idea. It's free and it might make a difference. Of course you then have to reset your clocks.
BTW I think the idea of switching the breakers on and off is a good idea. It's free and it might make a difference. Of course you then have to reset your clocks.