My car beeps.

Is the beeping sound coming from under the dash behind the radio and giving random beeps 5 at a time. If so, then it's your air bag module. Does your airbag light come on. If so, you may not have reconnected the air bag sensors after installing the turbos. Just one man's opinion.

Peace
Al

where is the ab sensor?

In the area of where one might be for turbo work, the crash sensors are in the front clip. Al can answer more on the rest of the system.

I think Al is right, though I have no clue about seatbelt beeping.

The ignition chime (headlights on, key not being turned to 'off', etc) should be constant. There is a tang inside the collar on the lock cylinder which either makes contact or doesnt, and it is a mechanical chime AFAIK. This sounds like it is smart, like an air bag.