In the half bath of the master bedroom I have a toilet with a Universal Rundel bowl that has been flushing happily since the sixties. Recently I began to hear a strange trickling sound after a normal flush. A few days later, after two flushes, water rose upward in the toilet bowl and then went back out of the bowl and out on the floor between the toilet and the floor. Can someone explain what is happening and how to fix? There are no other plumbing issues anywhere in the house at present. We are on a sewer system.