Synergy 2110 handset randomly making 'alarm' noise?

Completely at random one of my Synergy 2110 handsets will start making the most annoying 'alarm' type noise. Pressing any of the keys on the handset will quiet it temporarily, but it's necessary to remove the battery to actually stop it. Replacing the battery after an hour or two, the handset will usually be quiet again for a day or two before going off again!

Please tell me that there is something that I can do to fix this unbelievably annoying problem (being woken in the middle of the night is *not* fun), other than taking a large hammer to this handset.