random blue flashing screen + dual vibration + dual sonar beep

Hi, since i transformed my iphone (v4, IoS 4.2.1, jailbroken) with a white kit, i have a strange issue never faced before. From time to time, on a random basis, my iphone does a 1sec flashing blue screen + dual vibration + dual echo sonar like beeping.

It's not the usual signal for an email nor sms or notification, sound is different. And doesnt signal anything, just acts like that randomly. I wish it stayed quiet ! :)

I was wondering if someone would know how to fix this annoying issue ? already tried a search on the net, but not exactly documented. Also already tried a hard reset and a system reinstall, but unsucessfully fixed that.

I'm not sure if it's related to the white kit tranformation or something else...