Tank downsides

Not to sure about your first question. But a guess would be the risk of it foiling while rotating the turret. this would be far greater than the risk of a shell hitting that spot. Tank wheels were and still are covered in solid rubber. When you look at the real thing, you may well see chunks out of the rubber.

I can't speak directly for WW2 tanks, but I was a warrior driver for 6 years and I also trained as a gunner. When your in the vehicle with your headset on, engine running and you are busy doing your thing, you don't notice it to much. When we were on the static range, I would often have to sit in the drivers  seat while they were firing the gun above my head, and I often fell asleep.

Most wheeled AFVs/ APCs have "run flat" tires.. Those that don't don't generally get engaged by small-arms, since their primary purpose is not to attack enemy positions directly, but to get the infantry to a dismount-point to continue on foot as they over-watch with heavier weapons.

As for the "lip", some tanks actually did have that feature, but there was a tendency for solid-shot and capped HE to ricochet into the turret... Others had "shot traps" which were design flaws... Rounds would get "trapped" into the space between the turret and damage the turret-race, jamming it. I believe that's what happened with "Tiger 131"...

US tanks and most tanks in general have solid rubber road wheel rims. The only tracked vehicle that I recall that had inflatable road wheels is the M56 Scorpion (aka SPAT). It was a 90mm anti-tank gun on a basic tracked chassis and the big road wheels helped protect it during airdrop operations.

As far as sound, that would depend on whether it was a 37mm, 50mm, 75mm, 76mm, 88mm, 90mm, etc. main gun.

I have fired an M109A4 155mm Self-Propelled Howitzer and it is not really very loud inside. You don't get a lot of the "Boom", but get a lot of the metallic noised like the tube recoiling and the breach block opening.