This is normal for the Planet. Always has been. The feet do all of the work in isolating the player; so taping the top of the unit will cause it to skip. This in no way means something is wrong with your player.
Compare tapping the shelf it is on. The feet on the player will isolate it from this sort of "interference". My advice is to stop tapping it.
Compare tapping the shelf it is on. The feet on the player will isolate it from this sort of "interference". My advice is to stop tapping it.