How Do I Stop My Touch From Giving Audible Notice of Calendar Events?

I sync my iPod Touch with my computer -- for Music, email, photos, contacts and calendar.

When I have a scheduled event on my iMac I usually set an alarm notification for 15 minutes before the event.

My challenge is the iPod spends the night on my bedside table and if I have an all day event my iPod chirps the notice at 11:45 p.m. -- usually just after I've managed to fall asleep!

Ho do I keep things the same on my computer and iCal but not have the iPod chirping me away just before midnight?

Thanks