: I have an intermittent horn like sound eminating from somewhere in my house. Inevitably it strikes at night -- goes for about 10-15 seconds then stops. I leap up from bed, but it seems to come from everywhere and in the few seconds I have I cannot localize it! It echoes everywhere. This happens 2-5 times a night but only sometimes!!!! There is a variable lapse between the wailings of 45 minutes to an 1:15 minutes. I have 70 lbs of water pressure and tried everything so far including replacing the toilet flappers in every toilet. What else could be wrong?

Paul,
Causes could be:
toilets, check for flapper leakage and if needed, repair or replace fill valves. I have even had shutoff valves at the wall causing noise. You've already checked the flappers, so you are narrowing it down.

Icemaker could be filling at night.

You may have a pressure reducer on the incoming line making the noise.