Have a Krell 700cx and 801 Nautilus B&Ws using Krell Home Theatre preamp. Everything in system unchanged for 15 years. Suddenly now when I turn on amp I get bird tweeting sound from both speakers followed by hum. Checked speakers through other amp and fine. Know outlet is dedicated line meeting amp spec and checked it. Tried different dedicated line meeting spec and still get sounds. Not speakers, not outlet ground loop. Is amp itself the problem the problem? Still happens with all peripherals and preamp turned off. Ideas?