I know this issue has been addressed on other threads, but I can't seem to find a resolution.
I have been in my house about 18months - it is about 70 years old, but in good shape. Recently, I started seeing a ring of wet carpet in my semi-finished basement (i.e. previous owners put down thin carpet on concrete foundation) around a floor drain. The ring appears and gets worse whenever the washer is run, and I think when the tub drains from a shower.
Also, the tub and sink on the second floor bath drain very slowly.
When the washer drains, I can hear gurgling sounds coming from the floor drain, water backs up into the utility sink, and then eventually water starts coming out of the floor drain. I do have a washer standpipe that I installed shortly after I moved in.
This started happening about 6 weeks ago - I called roto rooter about 3 weeks ago, they cleaned out the main line with the power auger, and all was good for about 10 days. Now it's back in full force. They won't come back for free because I have a garbage disposer (which apparently voids their guarantee), but they will clean it out again for about half price. The first time they didn't find any tree roots or anything like that, but it seemed to work...now that it's back, I wonder if either a) it wasn't a full cleanout the first time (and the small hole that was formed just reclogged or b) there is some other problem than a blockage in the main line (vent issue?).

For reference, the cleanout where roto rooter cleaned out the main stack is the same stack the washer and utility sink drain into.

Thank you for any help or recommendations you can give.