Try one last thing before you box up your amp and send it away. Jctubes has a valid point about neutral and ground being swapped. I understand your electrician had a look, but nobody is totally infallable. Lord knows there have been a hundred or so times that I have caught myself after a second look. Go to your local hardware store and for maybe $10 pick up an outlet tester. This is not a test light but an outlet tester. The tester usually has 3 small lights on it. If you plug it into your outlet and it is wired correctly a certain sequence of the lights will light. If the outlet is wired incorectly a different sequence will light and the sequence can be decoded to determine exactly what is wired wrong. This inexpensive tool should be in every audiophile's toolbox. I also recommend if it checks ok to plug your amp in to one of the plugs and the tester into the other to test it under a load. I have seen a few instances where resistance in the ground path to an outlet has caused a problem and this can only be found when a load is placed on the circuit so current is drawn. The tester should be able to pick up this problem also. For less than $10 it is worth a try and if you do find something please don't blame your electrician as nobody is perfect and everybody has an off day now and then. Good luck.
