I called Bel today to confirm the audio ramp-up fix for my STi before proceeding to ship it for a reflash with the latest firmware. Unfortunately I found out that the latest firmware still produces audio alerts which consist of either slow or fast audio alerts, with no ramp-up in between. The Bel customer service representative didn't know if a "fix" would be forthcoming since the two stage audio ramp-up is by design.
I apologize for any confusion caused my my previous post on this subject. Until today I was under the impression that a new firmware flash was available which would give the STi a smooth audio ramp-up.