Knocking Noise When Pulling Away

Hi i'm new to the forum, i bought a 2004 A2 1.4 TDI SE Colour storm last year from an Audi main dealer, as i'm commuting 100 miles a day i needed a very economical vehicle. I return about 57mpg and i don't drive particularly slowly, anyway my gripe as such is that after about 2 months of motoring my car developed a knocking noise from under the bonnet, this noise only occured as i pulled away.....
I returned the car to the dealer and told him of my plight and as it was under warranty they did some fault diagnosis and said that the Exhaust gas recirculation valve had worn out, they promptly replaced the offending item. However, everytihng was fine for a couple of months and the noise started again so i went through the procedure again and had another valve fitted....since then i've had a total of 3 valves fitted within the year.
The car was due its first service last month and the noise was still present so i asked the dealer to replace the valve again to which they agreed...........when i picked the car up i asked if the valve had been replaced to which they informed me that they had not as it would be a waste of time but they did say they had lubricated it and the noise had dissappeared, to which i accepted.
About 3 days later the noise was back so i contacted the dealer yet again they were reluctant to replce the valve again which i understood, so i contacted Audi UK and informed them of the story to which thee reply was that they would contact Audi Technical and see what can be done...
A few days passed so i phoned them back to seee if they had found out any information to which they replied was that the FAULT on my car has suddenly turned to a CHARACTERISTIC and there was nothing that could be done.
Last week i was contacted by the dealer who told me that Audi technical had been in touch with then and there was a potential solution, which was to mount the valve on some rubber bushes and this would reduce the amount of noise being tranmitted through the chassis.
The work has now been completed on my car i still have a knocking noise as does a friend of mine who own's an A2.
This may sound that i'm totally against Audi and A2's nothing could further from the truth it's a truly wonderful car it has never let me down and is fun to drive and cheap to run what more could you want (No knocking noises).......I just turn the stereo up and all is fine