Noise when engaging clutch

Specs are 68 Dart, 340, A833, McCleod diaphragm clutch. The car has been on the road for two summers, probably doesn't even have 500 miles on it. I'm looking for some assistance in diagnosing an issue. Approximately half way through clutch engagement I'm getting an unsettling noise. It also also occurs intermittently when clutch is fully engaged, driving down the road. My first thought was a u-joint going bad because that is almost how it sounds, but I checked that out and everything seems fine, no play in the u-joints. Also, in addition to hearing, it can be felt in the clutch pedal. So I thought throwout bearing or input bearing, but doesn't that typically show up when clutch is NOT engaged? I did notice evidence of some fluid on the inside of the inspection cover when I removed it, but it was basically residue. If I'm developing a small rear main seal leak, would a small amount of oil on the clutch plates translate to what I am describing? I wouldn't have thought so, because it definitely sounds metallic to me. Any help diagnosing would be appreciated before I start pulling the trans and going fishing in there.