gurgling, flushing noise from overflow

My overflow has recently started making some loud gurgling and "flushing" noises. I have a Durso standpipe in place and haven't had any problems for the past year or so. The input to the sump from the overflow has only a slight bend and ends about 1 inch below the surface of the water in a bubble tower filled with LR rubble.
The noise is not constant (thank the reef gods!) but usually happens every night around 3am. Great timing.
Any thoughts other than throwing it across the room?

 

whens the last time you cleaned it? sometimes the air gets obstructed internally which will produce noise

 

You mean the standpipe itself? I don't think I've ever actually cleaned the whole thing. I shudder at the thought of taking the whole thing apart. But maybe that's what I need to do. Thanks!
Any other thoughts?

 

sometimes they come out of the bulkhead just enough to let water pass. maybe it came unseated. i take mine out every six months and clean em. reseating them can be interesting, carefull not to break the bulkhead.

 

"Interesting" is such a flexible adjective. It can mean so many things. I assume that in this case you mean "interesting" to mean "*****" or "pain in the arse"?

 

it can be, i have big arms and fitting them in the overflow is hard enough. but theres more than one way to skin a cat. i push the standpipe into the bulkhead hard enough to seat it but not to break the bulkhead, then twist and pull until the desired height without unseating it.

 

Do you have a valve to control the air intake? When I made my first Durso I did not have that and every once in a while I would get the drainage sounds. I made the air intake bigger, added a valve and after a little adjustment I had no more problems.

 

Right now I just have some airline tubing coming out of the hole in the cap. What diameter hole do you have on top of yours and how to you control the airflow?

 

i dont have an airline attached, the hole is about 3/16-1/4.

 

That's the size airline I have in there. Hmmm. Guess I have some dismantling and cleaning in my future.