One of the most noticable musician flubs I can think of is in one cue in Jerry Goldsmith's The River Wild, where you can hear a session player coughing or sneezing no less than three times!
According to Dutch folklore, that brings good weather.
Not sure if this falls into the category of errors/bloopers but there's some majorly audible inhalation action from the soloist going on in "Kara Meets Bond" from The Living Daylights.
