grey line on my optoma data projector

I have a really irritating fault on my optoma ep729 data projector. Seemingly randomly a grey vertical flickering vertical line appears running the full height of the screen about 1/5 of the way across the screen. The line is about 1cm wide.

After it has appeared, it remains even after disconnecting from the Dell 9300 laptop.

Sometimes it occurs after about 5 mins, on other occasions the projector can operate for 8 hours straight without a problem.