Reset '99 A4 radio from SAFE mode
 

I didn't find this when I searched for it using Google, so here it is
for those who may need it...

If your radio goes to SAFE mode (battery run down, etc.):

Turn on radio
Hold down FM2 and RDS together for five seconds.
You'll see 1000 on display.
Press preset 1 to advance first digit, preset 2 to advance second
digit, etc. until the correct code is displayed.
When the code is right, hold down FM2 and RDS for five seconds.

Good luck.