After flushing the toilet I can hear what sounds like water running for a moment underneath the bathtub right next to it. Lastnight while my washing machine was draining I heard the same noise under the bathtub. This time it lasted longer, obviously becase the washing machine drains more water than the toilet. This noise just started about a week ago. Could this be just a noise I shouldn't worry about or what? Would all 3 of those things share the same vent? Help please!

It sounds like your bathroom vent is blocked and your system's attempting to vent through the tubs trap. The sound you hear is air being pulled through the trap seal.
The solution would be to snake the lavatory roof vent. Put out enough snake to reach the base and 16 feet more. Good luck, Tom

Hi Wayne

It could be a clogged vent as Tom suggested but I would expect the sound to be at the tub drain and not "under the tub", as you said.

Is your home on a concrete slab? If so, it could be a leak and/or a clogged pipe. Perhaps you could cut an access panel into the wall and check behind the tub drain area. Home depot sells a cheap "snap-in" access panel for easy repair.

Otherwise, plan on renting an electric snake and see if you can gain access to the vent/drains.

Questions... let us know?

Mark