Buzz at termination of tremolo

I'm trying to generate an octave tremolo over several bars - there's an intrusive buzz at the termination of the tremolo that I can't get rid of.

If I terminate the tremolo on the bar line, this doesn't happen but my tremolo is supposed to terminate 3.5 beats into a 5/4 bar. The buzz problem on the built-in play function persists for up to a bar after the termination and screws up the timing. I've tried rewriting a couple of different ways and it still occurs.

See bar 3 of the accompanying file