micro bubble problem in new tank

hi, looking for help with a new tank set up. I just set up a 155 gallon bow front corner aquarium. it has a 30 gallon sump with a 1 1/2" drain line dumping into the sump on one end. it has a compartment for the skimmer a refugium and a separate compartment with a 2600 gph submersible pump with a 1" return into a bulkhead. as drain line enters the sump it makes a lot of noise and is full of bubbles. it has several baffles in the sump but most bubbles still make it back into the tank. it does the same with and without the skimmer running. I tried to slow down the return with a ball valve but the pump just sucks dry. should I try to throttle the pump down? any other suggestions would be greatly appreciated.
thanks,
dwthunt