Audi central locking is vacuum-operated. This makes the door lock plunger travel up and down in a smooth fashion.

It appears that Audi has completely redesigned the remote locking system for the 97 models. The 96 unit is a factory-installed option only and cannot be easily retrofitted by the dealer (without some serious hacking, anyway). The 97 unit is apparently quite modular and is now a dealer-installed option. The key fob is also different for 97, now featuring a "panic" button that did not exist in the 96. The 97 system apparently doesn't flash the blinkers and side marker lights when unlocking any more.