The appearance of Crack above window on outside wall

[BristolDeano]

Hello everyone, I hope that someone here may be able to give me some advice.
I have discovered a crack that runs along my outside wall, along the top of my lounge window and I don't know what to do, but need to do something pretty soon as is getting worse. Do you think it might be worth me sealing it up with some kind of filler until I can find someone to fix it? Do you think this is a job for a builder or window tradesperson? I have no idea why the crack has appeared. Fortunately, I can see no sign of water ingress on the inside. I have noticed that when it rains, I can hear it on my window and the window ledge which I can't recollect it doing before.

Any advice would be much appreciated. Thank you.

 

[Mr Chibs]

Can you post another photo(s) showing the whole window and above it, thanks.

 

[BristolDeano]

Here are some more photos. Thanks.

 

[ronniecabers]

How long have the windows been in?

Looks to me like the render ' edging 'has moved

 

[crank39]

I'm no builder but to me that possibly looks like they used a galvanised stop bead for the edge and when rendering up could have scratched off parts of the galvanising with their float causing it to rust and now its just blown causing the cracking, I would imagine its just a case of chopping off the same flat area of render and re doing it but this time using stainless steel stop beads

 

[BristolDeano]

Thank you for your messages ronniecabers and crank39. The windows have been in for about 6 years. I had a builder come around between Christmas and the New Year and he said the same as you crank39. At least I know it is not too major and the windows aren't going to fall out. I appreciate your time in replying. Happy New Year!