I currently have a GK Backline 600 head and a GK 4x10 cab. Anytime I turn the volume knob or boost knob I get this scratchy, in and out sound from the amp. Also if I hit a note, I get a muddy, in and out sound again. It only returns back to a normal sound after a long, constant turning of the knob to get a normal clean bass sound. I also noticed when my head temperature gets really hot with the fan going, I don't have this problem. Any ideas on what this is? Is it a simple fix, or something I gotta send out? Any input is appreciated.