iCal Alerting of Tomorrow's Events After Removing Alert

Devices affected:

• iMac (Retina 5K, 27-inch, Late 2014)
• OSX El Capitan 10.11.3 (I know I need to update to 10.11.4, but I need to finish some work first)

and

iPhone 6, version 9.3 (up-to-date)

Problem:

I have several calendars linked to iCal and some events alert me the day before at 9am. Most of the time, I don't want this. I know certain calendars do this, but I have not kept track of whether all of them do. In the past, I have gone in and removed the day before alert, but left the day of alert and after a period of time, it comes back! This happens on both my iPhone and my iMac. In addition, most new events automatically alert the day before at 9am. I have looked for a preferences option to stop this, but I can't find one.