I've changed my engine mounts 3 times on my 2004 A4 cabreolet and they fail within miles(start to vibrate & then within a week, severe knocking) the 2nd time, also changed the ****** mount, 3r

SOURCE: knocking when first start engine

Depending on the period of time and intensity of the knock ? If it is a rapid short ,loud knock then disappears altogether you may be dealing with a cam chain tensioner that is loosing oil pressure when the car is standing. A loose cambelt tensioner can increase the noise .

SOURCE: Audi A4 Quattro (2004) bumping/knocking from manual transmission

HI,IT SOUNDS TO ME LIKE THE TORSION DIFFERENTIAL ON THE GEARBOX IS CAUSING THIS,PLEASE TRY THIS,DRIVE THE VEHICLE TO A OPEN AREA,YOU MUST PUT IT IN 2ND GEAR AND DRIVE IN A CIRCLE ONE WAY ABOUT 10-15 TIMES,AND THE SAME THING CHANGING DIRECTION,THE REASON I SAY THIS IS TO LOOSEN UP THE TORSION GEARS,PLEASE LET ME KNOW,ANDY.

SOURCE: Vibration when I accelerate in my 2003 Audi A4 1.8T

if car shakes whilst acelerating and goes off when you let you foot off throttle then could well be a drive shaft cv joint

SOURCE: Audi A4 engine sputters/no power

Hi i know exactly what is wrong I had the same problem with my A6 change the air mass flow meter or sensor min was wher the air filter is sat writ on the top n£45 from eby good lich.

Mo

SOURCE: Audi A4 ESP light comes on and car shakes/vibrates strongly

I am dealing with this issue with my 2003 a4. The Esp Is your tractioon controll, which is tied into your Abs system. Your Brake light Circuit is also tied in, so. Check your Brake Fluid, all Rear Bulbs, then look into Abs wheel speed sensor. $100 bucks each. The yaw sensor is unlikely culprit, but the ESP Controll module which is located under glove box is most likely the suspect.<!-- from fixya rte -->