Why does my 2000 125 sx knock and rattle in first and second gears?

A knocking and rattling noise in your 2000 KTM 125 SX, particularly in first and second gears, may be due to several factors. It could indicate issues with the transmission or clutch, such as worn gear teeth or a failing clutch basket. Additionally, it might be a result of improper lubrication or low oil levels affecting engine performance. Lastly, check for loose components or wear in the suspension and frame that could contribute to the noise under load.