These are potential baseline sounds we can use to start a desensitization progression up to the scary sound. Listen to them away from your dog first, to get a sense of them.
I chose sounds from Apple devices since they are commonly used and a lot of people and dogs experience them. (I tried to get similar sounds for Samsung/Android, etc. but there is too much variety.)
These sounds are in order of frequency, low to high. (Lower is usually less scary.) Find one or two that don’t bother your dog the least bit. If you can’t, let me know and I’ll make something more custom.
Power Up iPhone
iPhone Classic Email sound
“Glass” (Mac version)
“Glass” iPhone version