In my experience, and from what you say, seems like this is more likely to be coming from a commercial premises rather than a private home.
Unless someone actually goes to the trouble of tracking it down, then nothing will be achieved, and you'll find it'll continue to activate.
Unfortunately, it isn't a matter for Police to respond to an audible alarm, especially when no one seems to know exactly where it's located.
Plus, the EHO "response" is also typical, again in my experience, even if it IS something within their remit.
If anyone can locate it, try to obtain details either of the premises and/or the alarm company, and that way someone with some responsibility for it may be tracked down.
I appreciate that this won't help you at the moment. Sorry.