Mine started doing that about a month now. I think its some sort of hourly reminder because it always gives 3 beeps 1 minute to the hour... say... 1:59, 2:59 etc...

This recently started when i made these changes:

Set a speed limiter of 60mph - gives one been as soon as i hit 60 mph ( kinda helpful and keeps you in check)
Set the Aux Vent for 6:00PM ( this is now deactivated, as in unchecked)

I am not sure what else i did... but now I know when the hour is approaching...