Worry not; it's a very common thing with miniature dachsunds and other small hounds. It's a bodily function to stimulate digestion and, yes, retain body heat.
Small dogs lose heat quicker than big ones. Maybe your dog is just cold?
My puppies used to do that when they were scared, or when there were a lot of people around that they didn't know.
I have a chi dachshund cross nd he shivers as well, I spoke with my vet the other day and it is nothing to worry about he/she is just fine it's just a small dog thing. :D
Maybe hes could or hes scared or nervous about something