If this AddOn happens to be trying to transmit a lot of information and you have a flaky modem then that could be the reason. A number of AddOns will silently try to send information over channesl to organize their visual appearance with other people who have that AddOn. The only Ace AddOns at the moment that handle unit frames are AUF and AcePerl, to the best of my knowledge neither of them does this.
Could you tell us which unit frames Addon you're using, even in PM? The best way to figure this out would be to take a look at the AddOn's code really and to see whether it's spamming a hell of a lot of data across channels anywhere.