(1) In a tape recorder, if the tape speed varies, the pitch of the recorded music will vary. If the rate of variation is fairly high, typically above 5Hz or so, it is called flutter. If the speed varies at rates below several HertzseveralHz, it is called wow. Flutter is actually a type of frequency modulation distortion and imparts a tremolo– or vibrato-like character to the music.
(2) See chatter.