water noise from overflow

[TheReefGeek]

When you mean the drain can't keep up, do you mean the overflow/drain can't keep up? Or just the gurgling noise? The gurgling noise can be quieted with a piece of airline tubing stuck down the drain to remove air.

If you are overdoing the drain line, (as in overflowing) you have no choice but to throttle back the pump or add more/larger drain lines.