Bongo Fury

Afternoon all,
The bleeper for the 'reverse gear engaged' and 'ignition key in lock' alarms has started acting up. It works fine 60% of the time, but will suddenly go, for want of a better description, wheezy sounding. It first showed up last week after I gave the van its first long run in my ownership, about 200 miles.
Is there a quick and easy fix? Otherwise it's hardly the end of the world and I can live with it.
Thanks in advance,
Mark

I would imagine the problem is in the sound module itself, rather than any of the inputs, examine the module its behind the plastic trim down by the drivers right foot.