I'm guessing you have one overflow drainline/hose feeding the trickle plate bioball chamber, and the other overflow drainline/hose just draining down somewhere else into the sump.
I would not restrict either drain line with a valve. You want the drains completely unrestricted.
The overflow that just drains to the sump is quiet. I'm betting it's a straight shot from the overflow to the sump.
The overflow that feeds the trickle plate bioball chamber most likely has the drain hose connected to a pvc elbow that attaches to the trickle plate square acrylic cover.
If so, this elbow may be causing the water to not flow as smoothly as the other drainline/hose.
Draining water may be backing up in this line somewhat, causing the water to rise in the drainline. When the water in the drainline get's high enough, the added head pressure in this water column/hose/pipe pushes it on through the elbow and you hear it burp as the drainline air passage clears. Each time this happens - you "see" the line sort of jump as you indicated.
This burping noise comes and goes every few seconds or so, and keeps cycling like this -over and over again.
You can try to eliminate this from happening, by reorienting the drainline/hose or using a straight pvc fitting on top of the trickle plate cover - getting rid of that elbow. Try to eliminate turns or sharp radial curves in the drainline(s).
As I said - I'm guessing at this point - not being able to actually see or hear it.
But it sounds very similar to what I've experienced myself.
