Faint "knocking" sound when window fully closed
I bid hello to everyone here! I am new to the forums and hope I could get some tips and help as I couldn't find useful help at my dealers.
I have recently acquired a 2 year old 318i E46 from an authorised BMW dealer. Everything is fine but I have come to notice a faint "knocking like" sound that seems to come from the driver (right) side doors. The sound is more obvious when the car is under tension, such as when it is just accelerating, braking or sudden jerk. There is usually a succession of 2-3 "knocks". The best I could explain is that it sounds like the window glass is knocking against something. I used to have squeaking sounds as well but I fixed that with some silicon lubricant to the wood trims on the door.
I have tried winding down the window and that seems to have stopped the sound. It seems that the sound is only there when the window is fully up. I have tried sending the car back to the dealers and they claimed to have fixed it. The sound was gone for the first day but came back after that.
I am wondering if there is anything I could do myself before I submit the car for another service review. Although the sound is faint but during long drives it really affects my mood, especially in a "premium" car as a bmw.
I have tried lubricating the window seals once but I am not sure of the right location or how to lubricate it effectively. I really hope someone could help me. I really don't feel like going back to the dealer unless I have no other choice. I was wondering if repeat treatment of lubricating the seals could help the situation as it worked with my trims. (I have to lubricate them 3 times) Thank you in advance!