Ok i've never had this type of setup before so I just wanna make sure this is normal. The tank has a wet/dry filter with an overflow box. The tank sounds... well like a coffee maker lol. The gurgle noise... it is normal?
If it's the overflow pipes that drain down to the sump all you have to do is stick a piece of air line tubing into the pipe and feed it out into air so it's not submerged in water and the gurgle will sees to exist.
Tube doesn't have to be long. One end in the tube deep enough to wear it's submerged by water and the other end just sticking out enough to wear it isn't submerged by water. It's an odd thing but it completely silences the gurgle. I have one in each of my pipe stands in my in tank overflow and I just stuck it in between the notches on the overflow so it stays there and just feed it out a hole in the back of my tank and it just hangs out back there where the light covers it so you can't see it.
I don't believe it would make a difference. I've never used a HOB overflow box but if you are getting the gurgle sound from the tubes sucking water in I don't see the difference. My in tank overflow has the pipe stands coming up, and then the water drains in them when it gets to the correct level. Just like the inside of an overflow box.