Odd gurgle sound from sink and collection tank vent pipe

[BlueWRXPride]

This has been going on quite a while now. From time to time there is a periodic gurgling sound that I can hear coming from the air vent under the kitchen sink, as well as the vent pipe on my collection tank outside. When it happens it's at a very regular interval, and goes on for a few minutes and then stops. I feel like it can happen at any time, even when no one is using the water. I've attached a sound clip that I recorded both inside under the sink and outside next to the vent pipe. Any idea what this is, and if it's an indication of a problem?

There seems to be some issues with the attached files, so here's some links:
Outdoor vent gurgle
Sink gurgle

 

[MicEd69]

I couldn't open your recording files, but a picture and/or sketch would help.

Do you have an AAV under your sink?

 

[BlueWRXPride]

Odd, not sure why the attachments weren't working. But I added a google drive link instead. Once I'm home I'll add a picture from under the sink, but since I hear it from the vent pipe I feel like it's more related to the septic collection tank than the sink.

 

[chinarus]

I have a rental house that has 3 feeds to the main septic line feed due to a renovation. The kitchen sink is on it's own feed to the septic tank and it would "gurgle" at times. After running a scope on the main line we discovered there was a separation/breach at the sink septic line junction.

Repairing the main line junction resolved the issue.

 

[BlueWRXPride]

Here's a picture from under the sink. I also got a picture of the air vent.

As a side note, I apparently forgot that just about 2 years ago I posted the same problem to this forum: https://www.plumbingforums.com/threads/gurgling-sound-from-air-vent-under-sink.20471/ At the time, I had the tank pumped and it seemed to solve the sound. 2 years seems like a little quick to require pumping again, but does it seem likely that is the issue once again? Or could there be some other underlying issue?

 

[Twowaxhack]

It’s sucking air. Install a real vent

Septic tank might be filling up and closing off any existing atmospheric vent, then it sucks air from your quickie vent.

 

[BlueWRXPride]

It’s sucking air. Install a real vent

Septic tank might be filling up and closing off any existing atmospheric vent, then it sucks air from your quickie vent.

What do you mean by a real vent?

 

[Twowaxhack]

What do you mean by a real vent?

A vent to the open air outside.

 

[MicEd69]

You have what I asked in my initial comment. That is an AAV, Air Admittance Valve, behind and above the bottom of the sink. It is supposed to let air in which would keep the sink P-trap from gurgling. If you can run a vent to the outside and above the roof, that would allow air to enter the drain and eliminate that trap from gurgling.

I'm assuming your collection tank has a vent open to the atmosphere without any type of trap, correct? The gurgling sound from that vent might be coming from the level in the tank blocking off the vent just like Twowaxhack indicated.

 

[Twowaxhack]

I suspect a partially clogged drain that’s not showing up because you may not be running enough water to completely fill the piping up to fixture level.

Check all your drain lines and tank for a back up.

 

[BlueWRXPride]

The house does have an air vent that runs through the roof, just not directly tied to this sink. I'm not sure if it's possible since it's essentially on an island.

Yes the collection tank has a vent open to the atmosphere. I assume that vent is in the ceiling of the tank, so if that is the case it'd mean my tank is completely full?

What's the best way to check all the drain lines? Hire a plumber to snake them all?