[Ange]

Have you noticed if her growling in usually around the same time every time she does it?
I noticed in your update your mentioned something about 2 a.m.
Between 2 and 3 a.m. is typically an active time for spirits.

My recommindation on what to do is this. When your yorkie is doing this,it is an indication that she is sensing a spirit. (If indeed this is what it is,and I feel pretty sure it may be) When she picks up on this, say aloud "You have passed over. Please go to the Light." Then ask your angels/spirit guides to protect you and yours and help the spirit that your yorkie is sensing cross into the Light.
Also ask that you and yours be surrounded in White Light.

Some people that pass do not realize that they have passed or feel they need to hang around for whatever reason.
Sending them into the Light usually takes care of this.

If you have any questions, I'll try to help.

Wishing you the best. Please keep us updated.