Whenever we use any water in our house we hear
This 'foghorn' sound it lasts only about 15 to 20 seconds. Any
Thoughts as to what is causing this? Just started today.

Could be the pressure reducing valve or a ballcock in a toilet. Try to pinpoint the sound by going to the PRV and listening. Just replaced one for a customer and that was the exact symptom.

Pop the lid on your toilets and check the tank level. It should be about 1/2" below the top of the white overflow tube. Good luck, Tom