323ci 5-speed transmission problem
When I start up the car and let go of the clutch it starts to make a light buzzing sound. I changed the transmission (5-speed manual) oil using Royal Purple 75W90 and it took about 1.5 liters. When I'm driving the car on first, second, third, and fourth gear when I press down the gas it starts to make a loud buzzing sound but it doesn't do it on fifth. When I am not on pressing down the gas it doesn't make that does. I'm thinking the problem is the transmission so do you guys know any fluids I can put in to get rid of that sound? Or could it be something different?