Be sure to review the first one on yelp after the second confirms.
What you're describing might be along the same principles but much larger, or it might be something else, but in any event it sounds serious. (No pun intended.)
Get a second opinion before a pipe bursts or comes loose, eh? If by "the outside hydrant" you mean a fire hydrant then I would call the city too.
Any chance of a video or audio clip?
Live on an acreage, and the outside hydrant is mine by the garden. Right by the well, which is a tube extending 111' straight down to a submersible pump.
In the utility room, the water service comes into a pressure tank. We just replaced the tank, and the sound began after that. The plumber insisted it was unrelated. Maybe a relief valve there would help...just a guess.
If there's no vibration that you can feel then it's probably alright. Flutes don't fall apart from their own sound. But we're talking about your plumbing here, where a failure can be expensive and inconvenient, so "probably" isn't that reassuring. It's just not supposed to be doing that.
> We just replaced the tank, and the sound began after that. The plumber insisted it was unrelated.
It's not impossible (that they're unrelated) but that sounds to me like the obvious culprit, eh?
It might be in your case that water hammer is triggering an oscillation in ... something. A valve, pipes that arn't strapped down?
There could be a dead end in the system (essentially a hammer arrester) that is full of air which water is sloshing into and shaking in the process.
What I think I'd try to do is isolate the cause. E.g. if you turn off the service valve into the house can you trigger it by opening and closing the hydrant?
Maybe you are triggering a _pump_ upstream from you?
In any case, if pipes are shaking or the pressure is obviously spiking then it increases the risk of failure... so it's not something that I'd personally want to ignore.