alarms sounds when unlocked with key

[fatboysmith1]

Hoping someone has had this issue resolved before, I have had my 2000 tahoe for a year now, my wife has a fob but I do not. I have always been able to unlock it with my key without the alarm sounding until a few days ago. The fob still works fine, and when the alarm does sound with the key I can still start the vehicle and it turns off. Like I said for the last year I have always been able to unlock with key without alarm sounding. Anyone know what might be causing this? Also it doesn't matter which door same thing happens.
Thank you