I have their tanks so pretty familiar with getting it to run quietly.
It is gurgling because the water level near the primary drain (shortest one) is too low. Turn the gate valve clockwise, maybe 1/8 of a turn at a time until the water level is near the top or just barely overflowing into the secondary drain, (the middle pipe) After each turn, give it 3-5 minutes for the water level to adjust, and keep repeating until it is where it should be. It should be near silent.
When I had my 75, I was running the Maxi Jet return pump with 5 out of the 7 of the blue lights on the controller box.
It’s important to make small adjustments to the gate valve so you don’t go to the other extreme with the water level so high it now starts spilling into the emergency drain. That adds even more noise when water starts flowing down it into the return section.
