Loud Sound, Bright Flash

Each night, some time after I've switched off the light (I'd say about 20 minutes after, but I'm not sure if it's always the same amount of time) and gone to bed there's this 'bang' sound that comes from the light fitting above my bed. I think the noise is caused by part of the fitting cooling down and at one point suddenly deforming. By the design of it, the light bulb actually touches part of the fitting, and consequently the fitting seems to get very hot.

Now what's strange about it all is that if I'm lying in bed when it happens, I see a flash of light. I'm pretty sure, however, that there isn't really any flash of light, and it's just a construct of my brain. There's been times when I've had my eyes open when the sound happened, and there was no flash, and there's something abou the flash that I see that makes me think it's a mental construct -- it kinda feels like what I'm seeing is "deeper" in the perceptual system than something that comes from the eyes, though I don't really know how to explain this. I'm not sure if I always see the flash, and I don't recall having this visual effect accompianing in sounds in other situations.

It's strange, but for a while I never thought about it being strange that I was seeing this flash of light. I'm wondering: how common/uncommon is this? I would not be surprised if it was quite common. I'm also wondering if this could be some sort of synthestisia effect, or whether it is it something else? If you're wondering, I don't think I have anything else that could be interpreted as synthestisia (and if you think it would be obvious whether you do or don't, it's not necessarily so -- my dad has been aware of synthestisia for a while, but it wasn't until he listened to some of the descriptions of it in a radio program he was listening to that he realised that he seem to have a mild form of synthestisia involving numbers -- it's apparently not all just perceiving things in terms of different types of perceptual sensations).