Noise issue from return line nozzle

[lel]

I’m experiencing intermittent bubbling noise coming from the return line nozzle at the top of my tank. Upon inspection, I noticed a small hole in the return line, located just before the dual flare nozzle. When I cover the hole, the noise stops, but I assume the hole is there by design and shouldn’t be blocked. This is for a 75-gallon aquarium. I’ve attached pictures for reference. Any advice on resolving this issue would be greatly appreciated. Thank you!

 

[Crabs McJones]

The hole before the dual flare nozzle i'm assuming is an anti-siphon break. So if your pump fails, instead of all the water siphoning back into the sump, the hole allows air in and breaks the siphon. Not sure why covering the hole would get rid of the noise though unless there's air getting sucked into the hole. is the hole below the water line or is it above it?

 

[lel]

I tried both positions with the hole below and above the water line. When it’s above the water line (as it should be I think) it makes constant bubbling noises at the nozzle ends. But when it’s submerged into water, it makes less noise overall, but does it from time to time.

 

[Cichlid Dad]

Hello, I would move that power strip if that is where you keep it.

 

[lel]

This is a hole I am talking about