Screen flashes BLACK while in sleep

Hi Everyone,

I have recently noticed (out of the corners of my eye at first) my iPhone's screen flashing while in sleep mode. I thought I was imagining it, or it was just a reflection, but after staring at it for a couple of minutes I realised the screen is flashing BLACK, like when you first turn it on before the icon appears, but only for a split second.

also, lately the battery has been draining very rapidly (very lucky to get 24hrs out of a charge). I was thinking these issues may be linked, such as an app not properly closing down, so I have RESTORED the phone and the screen is still flashing black every couple of mins (3 times while writing this, I'm a slow typist)

Anybody else noticed this? Any help would be appreciated.

Andrew