Under the rear cover of the transmission(yes, inside the transmission). I'm only familiar with the 2wd version, in which you must remove the crossmember and rear transmission mount first, and then a big ring of bolts holding the cover on, and you'll lose about 5 quarts of oil when you pull the cover.
The 2004 Audi A4 has 20 valves.
The 2004 Audi A4 is a gas-powered vehicle.
The 2004 Audi A4 has an inline 4 engine.
The 2004 Audi A4 has a 5-speed manual.
The height of the 2004 Audi A4 is 4 ft. 8.2 in. (56.2 in.).
The 2004 Audi A4 is 14 ft. 11 in. (179 in.) long.
The 2004 Audi A4 has a drag coefficient of .30 Cd.
The curb weight of the 2004 Audi A4 is 3252 lbs..
The 2004 Audi A4 has double overhead cam (DOHC).
The 2004 Audi A4 runs on premium unleaded (required).
The 2004 Audi A4 has 41.3 in. of front leg room.
The 2004 Audi A4 has 38.4 in. of front head room.