#1
I just got an Acoustic B100 100W bass amp today. I played it at Guitar Center and it was fine, and took it home. I got home, and plugged in. I was maxing out because I just wanted to see just how loud it was. On the amp is a light which shows if your sound is being distorted. It was distorting, but the light wasn't coming on. Then no sound was coming out, so I just turned off the amp. Now, whenever I turn it on it just rings out a note. I have turned off everything, and the amp even makes the noise when nothing is plugged in.
#3
Most likely a speaker issue, you should probably take it back considering you bought it today.
Gear:

MIA Fender Stratocaster
Jackson Kelly KE3
Ibanez Universe
Marshall JCM 800
Orange Jim Root Terror
Mesa 2x12
Ovation Custom Balladeer
pedals and such in profile