I was wondering what is that ringing bell that you hear in the AE86 while it's racing?

It's to tell you that you're going over 100?/mph.

Really, I tohught it was to tell you that you were overreving the engine or something like that.
Did it come stock? And USDM cars have that?

I know that some US Toyota/Lexus's had it, but can't remember which models. I don't think the US 84-87 gts/sr5 had it, your best bet would be to ask on club4ag.com. Funny thing is I was recently wondering the same thing because if I ever get a Ae86 I thought it would be interesting/cool to have in the car, so PM me back if you ever find out.