I go thru the same thing with Giz..poor baby. When I see a storm in the forcast I know I will be asleep at work all the next day. He jumps up in my face trembling running back and forth across the bed, I swear you'd think he was about to stroke out. I worry bout him while at work and it starts raining but my grown kids are there to hold him. Don't know what causes it, all you can do is hold him close and turn the tv up a little. Looks like the little goomers would stop and think, you didn't let the thunder get them last time.