Pro Clear 150 Sump Coffee Percolator sounds

Yeah, I think your suspicions are correct. If you're seeing the return flow increase suddenly, then taper off, and see that cycle repeating itself, it sounds like your return pump needs to be throttled back a bit. Basically what's happening is that your return is creating a siphon and it's manifested with the percolator sounds.

Put a ball valve on your return pump and throttle it back. You'll know that it's set properly when you can look into the overflow and see a constant water level for an extended period of time. It it rises and falls, then you need to throttle it back a little more. Repeat this process until you get your pump tuned into just the right amount of flow that you need.

--AJ