I've tried out four new '68 Custom Deluxe Reverb amps at four different music stores. When the reverb is maxxed, all four have a noticable low volume hum. It's not feedback, nor a buzz. Perhaps a 60 cycle hum; it's just a low volume bassy sounding hum when the reverb is maxxed. When the reverb is turned to zero, there is no hum. The hum occurs with both single coil & humbucker guitars & with various cords. The hum is low volume and does not increase when turning the master volume up. For most players turning the amp up to 4 or more, or not sitting near the amp, the hum wouldn't be heard, but the low volume hum is still there. But for playing in a small home tv room at very low volume, and sitting near the amp, the low volume hum is very noticable. Same scenario when I tried out one of the '68 Custom Deluxe Reverbs at home. Is this low level reverb hum a common thing with these new '68 Custom Deluxe Reverb amps? What can be done to remedy this reverb hum?..thanks.