my 190e squeeked like a church mouse after a belt change, it turned out to be the idler pulley. Try a bit of 3 in 1 on the idler or you could, with the engine running, spray some water from a spray bottle over the pulleys and see if that helps, the noisy one will go quiet for a while. That pre-supposes the squeek was there before you changed the belt but mine only started after a belt change . . . good luck !

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1993 190E 2.0L (Euro.) sold
1991. 500 SEL (Euro.)
1991. 300 CE (Euro.) sold
1993. 500 E (U.S. spec.)