I had the following rattles in my s3 and fixed them with WD-40 Specialist Anti Friction Dry PTFE Lubricant which you can get from Halfords for £5 and doesn't leave behind a mess -
- Dash rattle - my dash was rattling around the air vents which demist the windscreen, I couldn't pin point where so after removing the glove box and tightening screws and applying tape to different places I found the possible cause. I read on a forum that an Audi dealer gave a can of silicone spray to a customer complaining of a squeak and it worked. I used the above spray and it seems to have worked a treat, just spray it all around where the dashboard meets the windscreen.
- Passenger headrest - I could here a rattle next to my left ear and thought it was possibly the seat back loose but after further investigation it was either the headrest or the holes which the headrest goes in. I looked on the forums again and found one person had there's replaced under warranty, one who used the paper clip trick and one who used electrical tape. my method was to pull the headrest out and turn it upside down and spray the lube in and also into the holes where the headrest goes. I cannot hear the noise anymore.
- Window rubber noise - everyone with an 8p A3 knows about this one, it's when the top of the door frame rubs on the body of the car and squeaks. People use various fixes including the lube from VW and Einszett Gummi Pflege but it eventually comes back and the second one causes mess. I used the above spray and its gone but I don't know if it will withstand the test of time but its another bonus from just one product for £5.