This only happens occasionally, usually when I'm backing out of my driveway and I'm kinda manipulating the clutch, if you know what I mean, so the car won't stall. My driveway has a little hill to get up before the footpath so I have to go up slowly so I don't run anyone over, which means I can't fully release the clutch or I might stall. Anyway sometimes when I'm doing this I hear this really loud knocking noise, as soon as I hear this I always depress the clutch immediately which makes the knocking stop. It only happens when the clutch is like half way up and I'm accelerating. Sometimes happens in 1st when I'm taking off and slowly releasing the clutch. I'm thinking it could be a mount or a bearing or something?