A trumpet type sound when water is on

I have looked at several posts that talk about humming in the pipes but that doesn't exactly describe what I've got going on. So, I hope I'm not repeating a question that has previously been answered. We bought our house 8 mos. ago (newly built). We are on city water. When any water in the house is turned on we get what my husband describes as a trumpet like sound in the whole house. It eventually stops - most of the time - but is gets pretty loud at times and it is definitely annoying. We were out of town for a week and we turned off the circuit breaker to the water heater while we were gone and our neighbor who was taking care of our animals used the water to fill a water dish but I can't understand why that would be causing this. We didn't turn off the water at the main just the electricity at the box. So, we get the sound when we turn the water on - not off as most of the posts I've seen describe. Any ideas? The house is still under warranty - is this something I need to get the builder back out here on??? Thanks for any help/info.

Call the builder and have the plumber fix it while it's under warrenty, unless you want to pay for it. Why didn't you call when you first noticed it?

I had not called the builder yet because I had hoped it was something that would resolve itself like if it was air in the pipes or something. The builder's repair representative hasn't been very responsive to other items so far so I needed to know how serious it was so I know the appropriate degree of persistance to use. Thanks for your input.

Did you leave an outside hose bib on with a hose and nozzle attached? Sudden bumps in pressure caused by faucet usage can trigger this fog horn noise, the diaphram in the vacuum breaker will have a back pressure and cause it to vibrate just like a reed in a horn. The sound will resonate through your entire plumbing system. If it is not your hosebib it is probably a vacuum breaker in a toilet causing the problem. Turn off one angle stop at one toilet then test then try another toilet and so on, once you find the culpret you will probably have to adjust the tank level lower and or adjust the flapper. There are other causes out there but in my experiance these are the 2 most common.
Good luck