If I remember correctly the antenna is built into the back glass. Almost looks like the rear defrost grid. This is a very common for vehicles to not have "traditional" antennas and place the pickup unit in the rear glass.
The Vehicle does not have a blow off valve. so you will never find it.
The clue is in the numbers. 18t is an 1800cc turbo, the 3.0 is a 3000cc engine.
The 2001 Audi A4 has 20 valves.
The 2001 Audi A4 has an inline 4 engine.
The 2001 Audi A4 is a gas-powered vehicle.
The 2001 Audi A4 has a 5-speed manual.
The 2001 Audi A4 has double overhead cam (DOHC).
The height of the 2001 Audi A4 is 4 ft. 7.7 in. (55.7 in.).
The 2001 Audi A4 is 14 ft. 8.7 in. (176.7 in.) long.
The 2001 Audi A4 has 38.2 in. of front head room.
The 2001 Audi A4 has 54.7 in. of front shoulder room.
The 2001 Audi A4 has 41.3 in. of front leg room.