I have a three story house with one toilet on each floor. When we flush the toilet on the second floor the toilet on the first floor gurgles - not all the time. The one in the basement does not gurgle. What could be causing this?

When water discharges and runs down your pipes it creates a suction. This is why there are vent pipes to relive the suction and allow the water to run smoothly. When a vent pipe is blocked, the suction vents through the nearest fixture. In this case your commode. Your going to have to get on your roof and check the lavatory vent. I have found everything from birds nests to dead critters blocking a vent. Shine a light down the vent and see if you can see anything that may be down there. If not you will have to run a snake down the vent. I would recommend renting a Rigid K-60 sewer machine for the job. Open the 4" cleanout located just outside your house and run the snake out from the roof vent until you're past the cleanout. Hope this solves your problem, but if it don't, I'm as close as a click. Regards, Tom