A loud, percussive orchestral hit sample, used annoyingly for no reason in 80s pop music. The word is http://www.m-w.com/cgi-bin/dictionary?va=onomatopoeic, since the hits sound sort of like fwank! Most notable examples of use: Owner of a Lonely Heart by Yes, and Unforgettable Fire by U2. Example: 80s pop music can be dated by the sheer number of fwanks used per song.
FWANK
Meaning of FWANK in English
Slang English vocab. Английский сленговый словарь. 2012