Return back into tank making noise

So here's the deal, replaced my scwd last week and obviously the water rotates between the two returns that are in the fish tank. One on each end. The return on the left of my tank after it puts water back into tank and the water stops coming out of that return then makes a little gurgling/burping noise. Its like when the water flow decreases it is as if air is filling up the gap in the return. Never had done this before and started as I have switched out the scwd. Don't know if it makes any sense but thanks for reading. Was hoping it would work itself out over the weekend but has not

 

Are the ends of the return lines fully submerged?