I currently have a 75gal with 2 bakpak HOB units, a dual and a standard that I house my heater and other filtration in. I am happy with the performance of the units, however I am getting sick of the gurgling (for lack of a better term) noise that they make. My main reason for not using a sump is my stand is divided in half and has minimal room to do so.

1st are there any fixes to reduce or eliminate this noise?
2nd are there any other HOB syle that are quieter?
3rd if a sump is most solid option how small can it be and still be effective?

Thanks in advance for everyones input