Sometimes a very low level buzz that can be heard from less than a few feet away is considered normal. There are several other possibilities, let the amp warm up a while and it may go away or there is a light dimmer or some other control in the house that is causing this.
My Belles 350a makes a noise on start up then goes away after about 2-3 minutes. I had a 150a hotrod that made a slight noise at start then went away within a few minutes.
I consider this pretty normal stuff.
BTW, I wouldn't turn on the amp without a load. I don't think it will hurt this amp but some will do as Marakanetz above says and some will just blow the output transistors.
My Belles 350a makes a noise on start up then goes away after about 2-3 minutes. I had a 150a hotrod that made a slight noise at start then went away within a few minutes.
I consider this pretty normal stuff.
BTW, I wouldn't turn on the amp without a load. I don't think it will hurt this amp but some will do as Marakanetz above says and some will just blow the output transistors.