I just moved into my new home and I was noticing a gurgling sound coming out of the bathroom on my main floor. The plumber came by and took at it and made some adjustments and showed that the sound was no longer present. A few days later the sound started again and I made another call and the gentlemen showed up and noticed that the flapper valve was not sitting/sealing correctly in the reservoir. He replaced the flapper valve and the sound has disappeared! I'm very happy for their prompt service.