Fender Bass Rumble Amp crackling?

[diruikasu]

I have a Fender Rumble 15 Bass Amp, and it has given some grief lately. It has been crackling when I turn the volume past 5 1/2, and it sometimes crackles when I even have it on 2. I don't know why it does this. Sometimes right in the middle of playing my bass, the sound becomes dull through the amp, and eventually as I play it out, the sound returns to normal. I thought it was a bad cable, but I used another cable and still had the same problem. What's wrong here?

[WholeToneMusic]

Does it crackle while your turning the knob? Does it still crackle when your not playing anything?