I think its an air leak, take a look

[adl6009]

https://www.youtube.com/watch?v=80Su7DzdOxY&feature=youtu.be

I am replacing some of the cement around the pool soon so now is the time to repair this. I was hoping someone would recognize the unusual rhythmic nature and tell me something like "Oh thats a ..., just jump in and change it and it will be fine."
But I am pretty certain I'll be digging and looking for a hole or something.
The first part of the video shows the jets in the step, and when I open the vent you can really hear the glub glub, but even with the vent closed you can hear it. The end of the video shoes the pool return closest to that jet, while it tough to see in the video there is a pretty constant stream of smallish bubbles coming from there. The returns on the other side of the steps don't seem to have any air coming out.
This problem has been occurring for a few years. I have just replaced the pool heater and the pool pump and repiped that part of the system. That didn't fix it. Any ideas or suggestions would be appreciated. Thanks.

 

[duraleigh]

Air is being sucked into your system somewhere between the pump and the sklimmers. There is an article in pool school that talks about "Suction Side air leaks" that may help.

Essentially, the air get sucked in, then goes through the pump and into the filter. As it accumulates in the filter, it is blown out into the pool through your returns.

 

[adl6009]

You hit the nail on the head. Thank you. I took a look at the suction side and looked for the most likely suspect. The 20 year old flow selector valve stood out. So for $45 I got a new one for the suction side. Swapped out the old one and thats that. It was like I knew what I was doing. Thank you.