I don't understand why the gurgling. This year we've had a lot more precipitation than usual, so the sump has been running more frequently. Last year I had my main line rodded, repaired and a cleanout installed. Of course there were major plumbing issues at the time. There were no tree roots, it's just that the house is 60 years old. The sump pump is right under the upstairs bathroom plumbing and the mainline exits right under there through the basement wall and down to the public sewer line. The kitchen plumbing branches off upstairs, as does the washing machine and laundry tub just below in the basement. I've had no plumbing issues since the rodding. All drains run smooth. I do have two bathrooms upstairs and a bathroom in the basement. I recently added a kitchen in the basement, which comes off the plumbing by the washing machine. Could this be a venting issue?
It sounds like a venting issue to me. Did you vent specifically the fitting into which the sump pump dumps? Without a vent for itself the pump dump water is going to suck air from somewhere. Also, now in our area all basement type pumps have to be dumped into a vertical line. And I believe that vertical line has to be at least one pipe size larger then previously required. P.