We had an annoying and concerning intermittent humming in our pipes, so we once again called upon An Affordable Plumber for help.
As before, Travis came promptly and made a considerable effort diagnosing our problem, of perhaps an hour. He explained that humming in pipes can have a variety of causes, and that it's generally a matter of trying things until you track it down. He was very thorough in his examination.
Ultimately, he concluded that one problem we certainly had was that the pressure regulator valve for the water entering the house was not working properly. He noted a 16 PSI drop in pressure when a faucet was turned on, and said that that drop should be under five.
As with last time, we were not charged for the diagnostic process. Travis quoted us $1,030 to replace the valve. That quotation dropped to $930 when we said that we would take care of extending the existing water main wall opening by removing a roughly 30 inch by 18 inch area of drywall, in order to provide access to the pressure valve. (We actually had this done by the person who had finished the room that the valve was in. It should have been kept clear, but was not. It took him about 5 minutes.)
Travis came back a couple of days later and effected the repair, installing (I believe) a Watts regulator valve. It took him about an hour. After the repair, he demonstrated that the pressure drop when a faucet was turned on was indeed under 5 lb, showing that the new regulator was performing in a way that the old one did not.
Of course, there was no way to know if the humming problem was solved until some time went by, and we were able to observe its absence. Fortunately, the humming seems to have stopped. So Travis's diagnosis was correct, and the repair fixed the problem.
During the diagnostic process, Travis also checked to see whether various appliances had water hammer arrestors on their water feed lines. He said that conceivably the absence of an arrestor might also cause the humming. One of our appliances did not have such an arrestor, and Travis quoted $370 to install one. We decided to wait and see how the repair of the pressure valve fared.
Problem solved, quick service, and no more humming!