My plumbing is humming! help?

It started this morning, and has never done it before. It's a really loud, high-pitched hum and can be heard in the bathrooms. It only makes the noise when you're not using the water. Can anyone please help before I have to pay a plumber an arm and a leg to check it out? thanks.

Answers:
Its definitely not air in the pipes. Check the toilet. If the fill valve is leaking by a little, it will squeal loudly. Take the tank lid off and find the float. Pull up very gently and see if the squeal stops. If it does, install a rebuild kit. Very cheap and a easy install for the fill valve. I betcha this is the problem! Good luck!!

Other answers:
Sure, sounds like air in the pipes. I cant remember how to fix it but do a search. I remember it was pretty easy.
Sure, sounds like air in the pipes. I cant remember how to fix it but do a search. I remember it was pretty easy.
Not sure But could have an air blockage in pipes. You could try turn on all try turn on all the taps in your place. for a minute..then turn them off. It might work...Godd luck
that's weird... actually you could probably get good money out of charging admission, and then getting a bunch of bottles and filling them with different amounts of water, blowing on the rims of the bottles, and having the dog howl in the middle of it too... you could call yourselves The Leaky Pipes.

honestly, make sure its not coming from your hot water heater first, that might be making the noise, and then if that's not it... your dilemma sounds pretty strange. it sounds like a pipe somewhere is leaking or trying to bust while you have the water off. when the water is on, there's no problem with the pressure, so it doesn't make that sound. sounds like a plumber is going to be charging you an arm and a leg regardless, unless you don't mind having the water on just a smidgen all the time.
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