Why is there a buzzing sound coming from my amp?

I just got a brand new PYLE PRO P3001AT 3000 Watt Hybrid Power Amplifier and there is a buzzing sound coming from it.

Here are the characteristics of the sound:

It is the same volume no matter what.
It stops if I hit the mute button.
It is coming from every channel.
Adjusting the treble/bass doesn’t change the buzz.
It is worrying me :(

Here is the amp:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380205186971&ssPageName=STRK:MEWNX:IT#ht_3959wt_1165