air horn noise

[redrover]

Two questions!

#1 ranch house, 2 bath, flush master toilet, the tank refills, water stops then after a second or two a noise like a moderate air horn is heard for 5-6 seconds. This does not happen with other toilet in house. Any ideas?

#2 in looking for cause of first problem, under the house I found an air tank (about the size of the propane tank on my grill) attached to the water line. What is this? What is it for? Is it the cause of my noise in #1?

Thank you all!

[HayZee518]

Yhat tank is an expansion tank with an air bladder inside.

[LazyPup]

The Air horn noise is nost likely being caused be a defective fill valve in the toilet tank. Rather than quickly valving off tight it is slowly throttling and as the valve throttles down it dramatically changes the line pressures causing vibration in the piping. The solution is rebuild or replace the fill valve.

[redrover]

Thank You! Thank You!

I had decided the noise was either in the tank fill valve or the shut off valve. I took off the top of the fill valve and found what used to be a flat round black washer. It was no longer round or flat and wasn't much of a washer. The new one cost $.57, which seems like a lot for what it is. Replacing it solved all the noise problems and made my wife happy which makes my life easier.

Thanks for the help.