Behringer ACX1800 buzz from right speaker

[donnmon]

I've been using this amp for small gigs and its worked fine and quiet until now. I have a buzz(hum) coming out of the right speaker on this two speaker amp when I power up with or without the guitar and/or mic plugged in. I switched power cords and ran it through my Furman power conditioner with the same results. Any suggestions on what I should troubleshoot first? I appreciate any help, Thanks