We fit out a lot of suspension kits in our workshop and we find the common problems are the top rubber mount , i hate to say this but the T 6 ones ( newer design ) dont seem as strong as the T 5 ones we replaced 2 on a 35k van the other day , completely torn out .Did you ever find out what it was?! Sounds exactly what I have!
The bearing on the T 6 looks bigger and i think that is stronger .
The rumbling noise is the issue i refer too , If its a squeal noise that is more likely the Pump or drive belt ,
The problem is you can t see these things until the van is stripped ,