Nexus 6 Vibrates when turned on, at the google screen, vs one that doesnt.

I have restored my phone back to stock locked to exchange but one thing is confusing me. The replacement vibrates when the google screen shows up on the boot loader. Is the default and if so how do i restore this even though I have fully restored the phone via manual fastboot with the latest stock images. If this doesn't actually matter please let me know and we can close and lock this thread. Thanks