I was bored one Sunday nite and decided to have a look at the airbox after seeing the other thread. I took it out which was fairly straight forward. you have to un-clip a couple of wires and take out about three screws, just remember where everything goes and you can`t go wrong
Once the airbox is out, take it apart, remove the filter, I gave mine a good clean at the same time. I drilled about 15 1cm holes in the bottom of the airbox. It sounds really good, you can only hear it if I want you to! Anything over 2000rpm and it comes in, a deep low down growl
I don`t see anything wrong with drilling the airbox. I decided to do it once I realised that my A4 had a decent heat shield as standard, that was the deciding factor. If you need to fill the holes back up for whatever reason you can do
Go hav a play..