Charlie -
I love this post...I've heard a lot of reasons for getting out of vinyl, but yours is truly unique!
CD has a brickwall filter at 19,200 cycles.....vinyl doesn't. If you have a supertweeter, or even extended range tweeters and you play vinyl, you're dog will actually hear that which
we (ie., humans) can only 'feel' or sense.
Your dog
may be hearing an unnatural treble peak in the post-20Khz range. What cartridge are you using again? - and what is your MM section loaded at (47K) and what is the total capacitance of all cables from your cartridge to your phono stage? Seriously, the fix for your dog might well be properly electrically damping your cartridge so the sound is pleasing to him or her.
Ha - damping a cartridge so that your dog can stand or enjoy it - man, that's rich. Either I am or you are INSANE

John