I reckon they would've been quite noisey when they left the factory.....smoother....but still noisey by modern standards
sound insulation in the door and the adjacent side panel will help, as suggested.....other than that it's a relatively expensive job to get the mechanism sorted....rollers and blocks aren't cheap....besides which, who knows what sort of quality they are..... the lower sliding track needs to be dry and flat....any corrosion/grease etc. will make it worse.... Plus as the van is knocking on, everything will have moved relative to each other...there's only so much adjustment in the mechanism itself...the rest is down to physics as a quick test, you could remove the trim panel and stuff a pillow in it.....just to give you an indication of how much the door itself resonates
The slider track bottom and side are pretty good and clean - maybe blocks, maybe grease will sort it?
