Recently our toilet started to occasionally gurgle and when we try to flush it afterwards, it backs up and will not flush properly. Sometimes it will flush fine for a couple of days, then it will gurgle a couple of days in a row and then it won't flush right. The problem seems to be worse in the afternoon. Also, we are connected to a public sewer system. Don't know if that could have any affect or not. We have plunged and snaked the toilet and still have this problem. Any ideas?