Metallic grinding noise coming from my 147

[Hobes 147]

I'm getting a metallic grinding noise when I'm driving my 147 manual, it only happens when it is in gear and disappears when I put it in neutral or push the clutch down. It sounds like two metal plates rubbing together. I have no problems changing gears or anything and the car was serviced last month.

I've looked online and it seems like it could be any number of things, I just wondered what people on here thought it could be? Thanks.