Edwin here is my story!
After so many opinions through the internet from Audi Forums (of three different languages I happen to speak fluently), yahoo answers and taking the car to a professional mechanic. I finally solved the problem.
Audi dealer in Oslo Norway told me it might be the gearbox. Only bringing the car in to check what the problem is, was way much expensive. After which I cancelled the appointment. Yahoo answers and Audi Forums members got to tell me maybe it's part of my timing belt going. But how I just got my timing belt and water pump replaced two months ago. The mechanic should have spotted anything out of the ordinary. A professional mechanic in Gothenburg Sweden checked the car. Before he checked the car, he got to tell me maybe it's motor corrosion from the walls of the motor by using a different oil that is accumulated in the oil pan. But first I've to test the car to be 100% sure. After testing it he got the car scanned. Found no errors. He changed the motor oil and the filter. When I went there after three hours he broke the news to me. He tested the car by driving it, runs perfect beside the rattling sound. He told me what he did. Asked me to drive it for a week or two to see if the sound is less than before, he couldn't promise me that it will solve the problem. I drove 350km back to Oslo Norway from Gothenburg Sweden. The sound was still there even after what he did. By the way I took the car to Gothenburg Sweden (European Union member) cause over there it's way more cheaper to fix a car than here in Oslo Norway (European Economic Area member) which is way double price. It all happened three days ago. I gave up at last! Accepting the gamble to use the car no matter what gets ruined until I happen to go home to The Hague Netherlands to fix the problem over there on my vacation coming July.
I thought to give a try to two last opinions from Paul4all and yahoo answers members. Just like the last mechanic told you. Try changing to higher octane petrol. I use Unleaded 95 which my manual recommends. Not after two days ago that I tanked 30 liters of Super Unleaded 98. Guess what? It happens to have solved my problem.The weather is warm just like when the problem happens the most. Yeah am serious Edwin. So far so good. No rattling sound whatsoever. I also laughed off some peoples opinions just like you. But it costs nothing to give it a try. I wasted $500, not knowing and laughing off the real solution to the problem.
Sorry for the long story. If things come back or there is permanent change I'll let you know. Cheers.

 

yea alot of times the cheaper fuel will tend to cause the motor to knock. u might inquire to running seafoam thru the tank and swapping the fuel filter in the near future. Its really a simple process that anyone can do if u have two hands and a brain! unless u want the dealership to charge u a few hundred for 15 minutes of work. goodluck with the car!

 

Thank you for the tip Pau4all. You have been really helpful. If it wasn't your help I would've been wasting a lot of bucks for nothing. Been driving around lately. Things happen to be in perfect condition. I don't know how to appreciate you. I'll be changing the fuel filter in the future. Good luck with your daily routine too. Cheers buddy.

 

thats why we are all here! happy wrenching

 

Thanks for the Advice! I live in California and the highest octane of gas we have here is 91. Ever since I can remember i been putting nothing but the best octane of gas in my car. I'm going to do what PA4UL suggested and run the seafoam thru the tank and see if that helps... thanks again for the advice.

 

You are most welcome! Just give it a try. 'Cause we all happen to have had the same problem in the same season of the year. Which is not coincidence. Hope that higher octane to be the solution of your problem.
Be careful with the oil you fill, make sure it's specification meets VW specification. If nothing changes we're still here to help you through.
Just to ask. When was the last time you changed your spark plugs? Motor Filter?
Mine was in service last October '13. Changed both cabin and motor filter. Oil and oil filter and not to forget the spark plugs. Keep updating us. Cheers

 

just know that when u use seafoam u might want to swap the fuel filter over time. Cuz seafoam will losen debris and might clogg your filter. U can also run seafoam thru the intake manifold and also in the crankcase. But pour seafoam in and then do a oil change after to remove any thing that has loosened up.