Return is making bubbling sounds

[Brent F]

If it is making bubbling sounds it is probably getting air inside.

Solutions are to eliminate the source of the air or give the air a way to escape.

Hard to say what would work without seeing the actual system. An air line can sometimes be inserted to give air a way to escape.

Do you have large bubbles coming out of the return causing the noise? If so, a tee where the majority of water goes straight and the air goes up can eliminate the sound.