When the dishwasher, washing machine or toilets are flushed, one toilet that isn't being flushed sounds like a washing machine when it is agitating.

Our home is 10 years old and this has just started to happen.

Take the lid off that toilet and check the water level. It should be 1/2" under the top of the white overflow tube when the tank's fillede and the ballcock's shut off. If that's not the problem click back with more details. Tom