Sup guys. So i got a 2001 323i bmw, manual transmission. Yesterday i noticed a noise coming from the rear of the car. It makes a kind of knocking sound as if something was loose. But the thing is, it only comes up when u change gear and press the accelerator. Going through a bump or smt has no impact on it. Furthermore, it appears only until the third gear. Everything higher seems to be ok. Also, it seems it's only happening when u go up in gears. Getting from 3rd to 2nd, 2nd to 1st isn't a problem. I thought it might be the gearbox, but it's kinda weird, cuz i would think the sound should come from the front. Plus changing gears or the clutch itself doesn't feel that anything would be wrong with it. Any input on this would be greatly appreciated. I googled the shit out of it yesterday, but couldn't find anything decent, and i can only have the car properly inspected next week. Thanks.