DIY & Home Improvement

The upstairs and lower bath sinks are directly above one another. They are furthest removed from the toilet drain line. The tub drains are separate. So the only air these 2 sinks pull is from their own drains. The upstairs doesn't gurgle. The downstairs has the noise after draining out. Part is from the full trap, and it sounds like part is in the wall, higher than the sink. They wouldn't put a trap in the wall, there's already a p-trap at the upstairs sink. So I'm still suspecting a partial clog in the lowest part of the lower sink drain. Have to snake again.

Or maybe it's just the sinks are unvented. I saw a This Old House video, mentions a "cyclone" when the sink is full. Yeah, that's what I get in the downstairs sink. But the cyclone action seems to open up the drain some. It drains better after a cyclone, and even better if the water is just about boiling. Then in a few days it's back to the same old noises.

Thanks!