The Collaborative International Dictionary of English v.0.48:

Schnorrer \Schnor"rer\, n. [Yiddish, fr. G. schnurrer, fr.
   schnurren to hum, whir, hence, from the sound of the musical
   instrument used by strolling beggars, to beg.]
   Among the Jews, a beggar.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

schnorrer
    n 1: (Yiddish) a scrounger who takes advantage of the generosity
         of others [syn: schnorrer, shnorrer]