Flashing interior lights

[A8 3.7]

Can anyone enlighten me on why my interior lights sometimes flash on and off when either the front passenger door or rear door are opened, it doesn't happen with both drivers side doors. The only fault code was for the door contact switch rear passenger door but the flashing lights affect both passenger doors. Plus where is the interior light switches. The car is a 1997 3.7. Any info would be much appreciated.