A frequency audible only to English speakers and dogs

A while back I was eating lunch at my desk and cruising a cool website for tchotchkes (gadgets and toys). 

One of the items I found there, appropriately called 'The Annoyatron', was a complete waste of time and had absolutely no redeeming value whatsoever... except as a potential irritant and practical joke.  So naturally I had to have it.

(Update: No Clouseau... it's the electronic-looking thingy. The shiny coin is just shown for scale!)

Simply put, this little wonder can be hidden just about anywhere (e.g. under the desk of they guy who has been stealing your coffee cream and munchies out of the office fridge for the past six months).  It emits an incredibly irritating, high-pitched electronic chirp at random intervals of between 3 and 5 minutes.

The high frequency and relatively long interval between chirps make it virtually impossible to locate the Annoyatron... and it is pretty much guaranteed to drive the victim into a twitching, hair-pulling lather within an hour or two.

Or so I thought.

Apparently there is a cultural factor involved that I (and the inventors of this wicked device) hadn't considered.

When I tried it out at home, my wife and kids noticed it after the very first chirp, and immediately started looking around for a malfunctioning smoke detector or other electronic device.

Even our dog, Jordan, began slinking around and glancing into corners each time the thing let off a new chirp... knowing that something was amiss without being able to identify the exact source.

So annoying was this thing that within 10 minutes I had to disable it and fess up or face a full-scale insurrection from my household.

The obvious next step (to me, anyway) was to try it out on my carpool. 

I waited until I was in the car of the British Academic with whom I've been carpooling for a few years, to give it a try.  After the very first chirp he immediately reached over to start fiddling with the car radio and cell-phone holder to see if something was amiss there.

I smirked silently and continued to stare out my window at the passing scenery.

After the second chirp a few minutes later he asked me if I'd heard something... to which I naturally replied, "like what?".

By the third chirp he was rummaging around the dashboard and rechecking the hands-free unit to see if it was charging his cellphone properly.  Finding nothing, he again asked if I'd heard some sort of electronic chirp.

I just looked at him with my best 'are you hearing voices again?' stare and then went back to watching the desert landscape.

By the fourth chirp I could tell he was ready to pull the car over, fetch his tool kit from the trunk and start taking the dashboard apart, so I let him in on the joke.  Far from being angry, the first thing he wanted to know was if he could borrow it for his office.

Ah, a kindred spirit!

The next day I asked how the 'experiment' in his office had gone and he offered a surprising answer.  Apparently, after hiding it in the work space he shared with several of his colleagues, none of them had given any indication of having heard it. 

Odd!

It was then that a theory started to form in my mind, and I decided to test it out the Israeli attorney who frequently takes a turn driving our carpool.  Shortly after we were all settled in his car the next day, I set the little Annoyatron to chirping in my pocket.  I watched expectantly as our carpool mate sat quietly at the wheel for nearly 25 minutes without giving any indication of having heard the jarring noise.

When we finally asked him about it (it was starting to grate on our nerves and we knew what it was!), he gave a rather surprising answer.  It turns out he'd heard the noise from the start, but since it hadn't seemed to be bothering either of us, he'd simply ignored it. 

Very odd!!

After that I tried it out on several of my Israeli coworkers with the same result.  Nobody took any notice of it... except one guy who was originally from Canada.  He started looking around for the source after the very first chirp, and asked if I'd heard it after the second.  The Israelis, on the other hand, displayed a complete lack of curiosity about the new sound in their environment.

I'm baffled.  Is this perhaps a frequency that only annoys dogs and native English speakers?  Inquiring minds want to know.