From what I read on here it's a combination of low MDBF, electrical and suspension issues that's causing the early demise of all these NG Hybrids.
There has been random ENY XD40s that sounded odd in the interior recently, I just chalked it up as the B/O having the bus shifted into an different gear.
The B/Os even know the difference between Allsion and ZF transmissions? Like at depots that operate buses with both (Like JG and WF for example) do they even know the C40s and XN40 have different transmissions but the same engine. I always got the feeling that if it's not relevant to their job title, B/Os don't care about that type of stuff. Seems more like an concern for the mechanics.