Hello, I have a 2 story home. All the bathroom plumbing goes to a main pipe. There is a vent tube that goes through the roof also. After a heavy rainfall when the sump pump turns on the discharge the water that has came through the tile system the toilet bubbles and gurgles. Now that the rain has stopped when the washing machine drains you hear a gurgling noise and the toilet water level drops. What could the problem be? Do I have a blocked sewer main, or is my vent tube blocked. It has been doing this for about a month. Any help would be great

This is strange because your tiles and sump pump should have absolutely no connection with the sewer system. Is it possible that someone has connected your sump discharge to your sewer line? Should not do this.
When the washer drains it is causing a siphon effect which leads me to think your vent is partially blocked. That is why your toilet water level gets lower.