Just before a thunderstorm breaks, it’s often commonly seen how a dog will seek lower ground. Whether a basement or behind plumbing tubes, it’ll likely be making a beeline to these types of places.
While we could easily attribute noise as the main culprit, that’s just half of the answer. Noise phobia could develop in dogs according to how they’ve been exposed to stimulation during their upbringing. While posing no real threat, a sudden loud noise would trigger an irrationally intense fear, which will also be seen in other settings, like with pyrotechnics.
If not treated, said phobia will eventually get worse. Partly due to its created instincts in always feeling the need to be alert to its surroundings, sudden loud noises could make the dog confused enough to have it believe that a flight/fight response is needed.
Other things that could heighten this type of unhealthy response could be related to genetics, caretaker behavior under such circumstance, changes in atmospheric ions &/or barometric pressure, as well as static electricity.
Try leading the affected canine, gently, to inside an empty bathtub, while being careful to not show human apprehension towards the same reason dog’s getting irked. The bathtub’s ceramic material also helps by blocking static electricity.
Of note, (even though it may sound counterintuitive) also keep in mind not to talk to the pet too much in a reassuring way during this process. The way in which a dog understands human-speak may lead it to think that this is a type of behavior that should be repeated in the same situation.
No bathtub? Then try a quiet, dark room. Maybe also add some relaxing music (I’d recommend something with a heavy string emphasis due to its positive effect on beta brain waves). If the dog has gotten used to rest on an enclosed space (e.g. a low box), that could also work.
There’s now a spandex-like jacket made for dogs that has been shown in some dogs to decrease anxiety under doggie’s stressful situations. Called the ThunderShirt, it’s adjustable to fit most sizes.
Another related strategy to the quiet, dark room, is to make it more so by closing all window blinds &/or curtains. Leave a light on, which could help mask the random storm light flashes. While some recommend canine anti-anxiety prescription med, I would stay clear from it, but for extreme cases (severely neglected dog, etc).
Pheromone applications may work in some cases since it addresses smell & instinctual communication between dogs. Same goes for essential oils (lavender, perhaps), or even herbs in/as a dog collar.
It’s not about a dog choosing to be afraid in such situations. It’s just an inherent reaction toward something that doesn’t seem to make sense as compared to their day to day. So don’t think of your canine as ‘damaged goods’, but as an opportunity for both of you to further bond.