I'm currently running a Behringer UltraBass 300-watt head with a 4x10 Hartke transporter cab. I noticed not long ago that the cab has developed a hissing sound. It was tolerable not noticeable in a live setting but it's gotten to the point where I can't play a live show with the cab. I've used the head to DI into a PA and there was no hiss so it's not the head. Neither of my basses are the issue because those have been tested in other amps. I don't think the speaker is blown because I still get good tone but there's just an overlying hiss over everything. Anybody have any suggestions?