It is possible the main transformer down his street shorted a winding about the time of the installation and that is the reason he is having sound quality problems. There isn't anything in the ATS that can clip a 120VAC sine wave but if he really has a clipped sine wave, it would have to be the transformer at fault. He wasn't running from the generator at the time, so that is not the problem.
Or, as I said before, it could just be all the EMI in the ATS is flowing into his system.....
Or, as I said before, it could just be all the EMI in the ATS is flowing into his system.....