I just received a new DSL100HR. When I turn it on I hear a constant 720hz ring directly from the amp. 

It does not change when I move any knobs, have it plugged into my attenuator or speaker (16 ohms), or switch outlets. It happens on low, standby and high settings. 

I found a YouTube video (You can hear the ring @1:12seconds) and he describes the same ringing but apparently that amp also had volume issues that mine (to the best of my knowledge) does not. The amp sounds good but I haven't played a Marshall before.

Should I be worried and return the amp?

YouTube link was necked but it it is titled "Marshall DSL100HR Keeps Blowing Fuses - Tales From The Repair Bench"