Pulsating Water in Toilets?

We have recently noticed that the water in all of our downstairs toilets is "Pulsating". The water recedes down the bowl and comes back out again every second. It goes down about an inch. I think the overall water level in the bowl looks lower than usual too.

Any ideas?

Thanks

Is it really windy right now?

No

No, it's not windy, but it's been happening for about 3 or 4 days. I kept hoping it would just go away..

Maybe the New Madrid fault is starting to slip a little and you have your personal earthquake warning system.

http://hsv.com/genlintr/newmadrd/

On the other hand, you may be getting a vacuum on your sewer outlet or a problem with your sewer vents. There could also be a pressure difference in your house due to ventilation systems.

The period of cycling is probably related to the natural frequency of the slug of water moving back and forth in the bowl, possibly until it breaks the trap seal and then moves back by gravity.

Try opening a window in the basement and see if the surging stops. That will equalize the pressure between inside and the sewer vent that goes to the roof.

Then put in some water to fill the trap but not enough to start a siphon and see if that makes it go away.

You also may have a partially obstructed drain downstream.

Put some water in the bath tub and fill the sink, then let them drain at the same time and watch the water level in the toilet.

If you get a reaction, then look to clean that part of the drain.