Troubleshooting occasional popping from solid state amp?

Open up amp on bench. Connect to small test speaker. Power up. Use insulator like thin dry wooden rod to push on board and connections until faulty joint is found. Use freezer spray too. Look for leaky electrolytic capacitors. Consider replacing them.

What I noticed is that the volume pot makes a pop when it's touched, could this mean the pot is the problem? Could be a grounding problem of the pot? Any advice on how to check it?

Yes. Could be a bad connection on the pot. Replace the pot - or, try contact cleaner spray if you're happy it's not a bad joint.

I noticed also the amp pops when the fridge turns on and off, any solution to this?

Identify which channel is involved. If it is both you have a power supply problem. I doubt a cold solder joint as that would have caused trouble a long time ago. I'd be more inclined to look at capacitors. You can replace them yourself by getting the value and rating then you can order the part from Digikey. Do not just heat up the joints and try to pull the cap out. Use a solder wick or sucker and remove all the solder then straighten the wire and gently remove the cap. You do not want to break the copper foil. 

Good luck,
Mike.