Mild grinding / machining noise

[Rajmun340]

I've had this noise for years, sounds like a mild grinding noise, but strictly only under acceleration. It disappears completely if taking the foot off the throttle. It's best heard under light acceleration because engine noise will cover it.
It's like a churning noise as if abnormal friction is occurring between oiled surfaces (it's a low frequency sound). it seem to come from the transmission or front of the car in general. I am assuming it's the clutch (6MT). The car also has a symptomatic clutch response. The clutch engagement is not smooth, it suddenly grabs and suddenly releases instead of progressively. This causes a tendency for the car to buckle when accelerating from a stop. I am the original owner. Car is very low miles, never abused.