I've noticed that when using my smartphone the vibrations from my actions aren't picked up, or are picked up very faintly by the microphone. I've worked quite a bit with microphones and I know it must be a non-trivial problem. Does anyone have experience in this arena?
The microphones are generally mechanically decoupled from the housing.
If the mic is in the housing then it is usually in a soft rubber boot that reduces noise from carrying over.
If the mic is on the board, then there's already decoupling from all the mechanical barriers (noises have to go from the housing to the PCB to the mic, and there are losses at each stage.)