I have an 8330 and I have the alarm set for Weekdays @8am. It works as it should. But also every day at 9:03pm the phone will vibrate 3x and then ring 3x. I have no additional alarms downloaded. Can't figure this one out....
I was thinking calendar or task alert, but you say nothing pops up with the alarm/alert.
The only other mystery alert that comes to mind is an application like twitter, a weather app like weather bug, an RSS reader like the WSJ reader or Viigo ... But that wouldn't be regular and it wouldn't necessarily be once a day.
And if someone was sending you a message at the same time everyday, it figures that you would see the message and figure it out.
I'm leaning towards the theory that it's some sort of inadvertant calendar or task reminder that you've set with a daily repeat, but I can't come up with an explanation for why you wouldn't see the alert message to open, dismiss or snooze.
The curve 8350i alarm is off/daily/weekdays. not one event. good for wakeup everyday.
For parking meters I use the alarm that changes every time I park somewhere else and clear the daily alarm at the end of work day because it's easier to set. For only one notification use the calendar instead.
Nextel 8350i ver5.0.577 (Southern Linc)
Open your active profile for editing, and see if you can find something that is set vibrate and ring in the manner you are observing. If whatever it is is an alert, it will be there. Or else it is an alarm.
Do you have the ability to set a new alarm in calendar? (I don't know what OS version that was introduced.)
Open browser, then menu, bookmarks. Scroll down to the Browser Channels folder and expand if necessary. Take a look at what you have there. If a browser push service like news or weather, or whatever, was set up on the device, that is where you will see it.