What would be a german crews reaction to being blasted by an american .50 cal? although none would likely pierce were they good for at least distracting the crew?
Would the Noise of vibrations of being shot by several automatic small arms be enough to cause some sort of panic thus lowering a tanks effectiveness?
Tanks were "buttoned up" when artillery or small arms fire could be expected, and normally the tank would be immune to small arms fire and shrapnel from artillery shells. A well-trained crew would know this and should not panic at the sound of shrapnel or small arms fire hitting the tank - rather they should focus on finding the source of the small arms fire and put under MG fire themselves, or place a high-explosive shell in that machine gun nest. A "buttoned up" tank was much worse at spotting enemy infantry and vehicles, as it had only slits or periscopes with narrow field of visions to use.
A tank was a noisy place to be in even without enemy small arms fire hitting the armour., The engine, the suspension, the gearbox, its own machine gun(s) and main gun would make massive amounts of noise. German tank crews were equipped with internal radio for this very reason and would be using throat microphones, allowing them to communicate with each other even with extreme background noise.
While a .50 machine gun would not penetrate armour, there are other things it could do to a tank. It could damage the supension, track or roadwheels of the tank, rendering it less mobile or even immoble. It could damage gun sights, radio antennas, periscopes, machine guns, tool boxes, reserve fuel tanks, air intakes and perhaps even jam the turret rotation or gun elevation/depression. All of which would render the tank less effective in combat.
It gets difficult to look out of a tank from inside. While crews were are trained to fight buttoned-up, the lack of a good outside view cuts you off from quite a bit of the battle, limits communication, movement, and coordination, and can be deadly in close/urban environments.
It could be especially loud depending on the tank, but I never really hear about it being debilitating. Suppressing a tank with small arms is essentially the same as suppressing an enemy on foot: You are denying them the freedom of full movement, which is an important part of battlefield control.
As an Aside: Going by observations from Yeide and Zaloga, .50 cals were often neglected by tank crews due to low ammo storage and the fact that they were mounted behind the commander's hatch. Even when moved in front of the commander's hatch, they were rarely used because it was just plain dangerous to do so (M10/M36/M18 crews used them once remounted, though, usually due to having no other options for crew protection). Third army liked them enough for a few tanks to field-mount them co-axially, but that was from late '44 on, and most tank-mounted .50s went un-used.