I’ve tried singing to them but DH said this is animal abuse LOL!! :-P
I worked for a vet and this was a common concern of dog owners. He suggested getting thunder and lightning music – yes you can buy this. On a day it isn’t raining start it off very, very quietly and very gradually turn it up loud. He also said to behave ‘normal’ so your pet picks up on your calm vibes. I haven’t done this but many of his patients said it worked for them.