As aircraft is accelerating it´s wing´s center of pressure moves aft, this unbalance the equilibrium mantained with CG that cause an strong diving tendency (tuck under) in order to avoid that, lots of a/c are equipped with Mach trimmer. MD-80 is another good example.
I think overspeed warning doesn´t have anything to do with AoA, it will sound to avoid inadvertent excursion over Mmo. This could produce a shock induced flow separation that may result in a contol surface buzz and loss of elevator and aileron effectiveness.