Recently after I unlock any door, there's a faint humming sound for maybe 30 seconds and then it stops. I'm assuming this is a door lock motor of some type. I had my vacuum pump replaced last year so I would assume that is out of the equation.

I don't think it's the antenna mast motor because I don't hear it on that side per se but it's possible. (Plus I lubed my antenna so it would open/close easier without sticking).

Any ideas?

1991 300d, 228k