Motorola Barrage V860

Has anyone out there had the problem we are having with 5 Barrages where they will emit an audible - but faint - busy signal? This happens only when in standby mode and will continue until the user opens it up and hits the end key. Verizon & Motorola Tech Folks can't yet find a solution??? 4 of the 5 are using the PTT feature - law enforcement... No pattern as it occurs at random sometimes 15-20 times per day, or maybe only 1-2 times per day? Also it does not matter where the user is?
Thanks for any ideas...