The 190E in the 90's had whining problems! Esp the 2.6 cars. There were several mods to subframe mounts & even installing a sound deading BLANKET under rear seat. However it sounds like this noise has just surfaced? If so you should have it checked by technician, pinion bearing failure can cost $$$.
MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V