I'm trying to figure out the same thing at the moment. 3" BDL setup on a 5 finger hub, caged clutch bearing & retainer. Normal rattle when disengaged, no slip & shifts nice when rolling, but when moving off from a standstill it makes a horrible screechy-shuddery sound.
It hasn't always been like this, kind of crept up gradually, so I guess something's wearing/worn out. I can feel some very light wear on the fingers, not notchy but there. The dogs in the basket are fine. Mainshaft support bearing is good & fairly new plates, both frictions & steels.
I've done a bit of searching on various forums & the there are loads of different opinions regarding causes & fixes, most seem to involve throwing money at the problem, not an option for me these days. I know this setup can be good, it worked with no problems for at least 20000 miles, so if anybody can shed some light on which component is the most likely culprit I'd be very grateful.