Strangrey line

For quite a while ive had this odd grey line down the right hand side of my monitor. For the most part it hasnt been that noticeable so i have kind of ignored it. Lately thought, it has really been annoying me.

I have recently upgraded the majority of my hardware, (cpu , gpu , psu , motherboard) so i am ruleing these out. The ram im using is from an older computer that i bought ready built, so at first i thought it may be a fault with that, however i have checked each piece by removing it individually, and each time i did, the grey line remained.

So the only thing i can think of now is a fault with my monitor, or possibly the VGA cable ? The fact that the grey line isnt always there, and dissapears sometimes, is also confusing me. Does anyone have any suggestions ?

Many thanks in advance
Matt