Peavey 5150 combo guitar amp - troubleshoot, repair, ocean / wave sounds

I purchased this "96" 5150 combo amp off craigslist and a week later it started having some issues. First, the sound level started fluctuating, loud to quiet. Then, it started making a sound like "waves crashing" everytime the standby switch would be flipped on/off. I figured I would make a video featuring the odd sound and my attempt at troubleshooting and fixing the problem. Maybe this video will help someone out in the future!!!