what makes radios drift from the proper tuning?

I have radios that I tune and after they play a while the tuning needs
to be adjusted.

This is common, I assume.

What is happening? Does the vibration make the variable condenser shift
a little bit? Or do the parts get warm and some value changes?

Is this more common in AM than FM? or vice versa? FM has AFC but iirc
AM doesn't have that.




I am going away for a while and I want to use timers to turn on lights
and also a radio, but some radios get so far out of tune, even when I
don't touch them, that almost nothing comes out, and I'd like the radio
to continue to play the station clearly.


I can't use radios with electronic tuning because with a timer that
turns the power off and on, when it comes on, the radio doesn't start
until someone pushes a button.