the title pretty much says it all…
cuz it sounds very similar to dog howls, especially high pitched coyote or wolf howls. My aussie is hilarious when he does it. He puckers up his mouth and sticks his nose in the air.
Oddly, my old dog (a beagle) used to howl every time a UPS truck drove by. She just went nuts whenever one stopped at our house. I always wondered what made her do that.
UPS standardized on turbocharged diesel engines. The turbocharger gives a light siren like note to the exhaust. To a large extent this is masked by the other exhaust sounds and clatter of the diesel engines, but to a dog it may well dominate.
I’m guessing if anyone in the neighborhood has a bombed Powerstroke, that’ll set him off as well. Neither of our dogs is howlers, but one of them won’t walk on the passenger (exhaust) side of my pickup if the engine is running.
Wow - this is the question I first tried to find the answer to on the SDMB.
Many, many moons ago.
Well that explains why dogs howl and sirens, but why do they bark at train horns? When the train comes through my town blowing its horn every few seconds, most of the dogs in town start barking. You can hear 20 to 30 different ones barking from all over the place. I can’t imagine a train horn sounding like any sound a dog makes.
There is something evil, evil about the Men in Brown. My Labrador knows it. All truly aware dogs know it. We just haven’t figured it out yet.
One day they will be taking us away in boxes, not leaving them. :eek:
My dogs don’t like my bagpipes - the basenji howls, and the dachshund yaps frantically.
I call it “Sonata for Bagpipes, Basenji and Dachshund.” 
Hmmm, my last cat didn’t like my saxophone. He’d hop up on the piano bench next to me and yowl and if I wouldn’t stop, he’d actually start biting my arm. I wonder if it sounded like a cat yowling to him. (to be honest, I’m a pretty crappy saxophinst…)
I’ve got a friend who’s a flutist, and she used to have this chow who would howl along with her every time she’d play. The thing is, he clearly loved doing this; he was overjoyed every time she got out her flute. She used to pull it out during parties to amuse us all. It was great.
We live close to a railroad track. The coyotes that live on our land howl when they hear the train whistle.
When we lived in Oklahoma, my mom was in the Church choir. Being a Catholic church, our choir sang lots of songs in latin , and my mom sang one of the higher-toned parts. Anyhow, when she was doing housework, she’d start singing her choir songs, and our dogs (A beagle and a dalmation) would start howling along with her. Was highly amusing.