That sounds a little rough, my initial thought about the problem I'm having is chatter along the flywheel.... Yours sounds a little more intense. It could be a stretched clutch cable, not holding enough tension. Just a thought
Its nothing good for sure. I would stop driving it and get off the ground to get some eyes on what it is before it really becomes a problem. When my throw out bearing went out I could feel it shaking through the pedal and hopefully that is all it is for you.
It has a new clutch in it also I need to get a quadrant cause I got it tight and it grabs so high it doesn't engage all the way but I'm gonna pull the cable off and look in there. Should the clutch fork move at all