Chirping sounds coming from the engine, usual are caused by the multi-belt. You can check this with a candle(light)...push the candle(light) against the inner side of the multi-belt whilst the engine is running. The wax of the candle light will get rid of the chirping sound.
This solution is (usually) only good for a short time and the chirping sound will probably come back within a few days/weeks. By the you know for sure that it is the multi-belt causing the sound and you will have to find out whether it is caused by a worn multi-belt or a bad pulley.

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)