Hi all! I live on the 2nd floor in a condo building in the Chicago Suburbs. Below me is the garage, and three units above me. So my kitchen sink has 3 sinks above in a stack. My sink drains fine, no problems. But, at least once a day, I will hear a loud gurgling sound from the kitchen sink, followed by foam (soap suds) seeping up through the sink drain. At some point I tried to seat the strainer/stopper in the sink to stop it but the pressure just popped it out. That particular time, when the stopper popped out, it was dirty water that came up instead of suds. Right after the suds/dirty water comes up, I am able to rinse it back down the drain without a stopped or slow drain. Any ideas as to a possible cause and solution?