Yes - if the rearward part of the block engages first the block is forced round, then snaps back and repeats - that in essence is the vibration that causes screeching. Having the front part engaging first allows the block to engage but never gets the grabbing. Play in bosses definitely doesn't help but you can still get screeching from the block, canti and boss flexing under load. All the extra play and linkages in parallel push definitely makes it worse.
