GK Backline 210 makes crackling noise when playing in low register

[jp9000]

I've got a GK Backline 210 that makes crackling noises as if I have a faulty cord or output jack, which I do not, when I play a note below C in standard 440hz bass guitar tuning. It also makes crackling noises when i adjust certain EQ knobs, such as: contour, and hi-mid. Anybody have any idea what the problem is and how to fix it?

[Jazz P Bass]

I know it sounds simplistic, but did you try cleaning the pots?
DeOxit is the very best.

[jp9000]

Thank you. I am going to try that as well as tightening up all my hardware. I just got this amp in a trade. I noticed one of the speakers have been replaced. I doubt its the 16ohm speaker necessary, being that most amps similar to this use 2 8ohm speakers for a 4ohm load instead of 2 16ohm speakers for an 8ohm load like this one. I imagine incorrect impedance could effect the performance as well. I plan on replacing both speakers as well as cleaning/lubing with deoxit and tightening all my hardware.