This has happened maybe four or five times in the last two weeks and it's starting to really worry me, when I'm slowing down for a red light or a junction and the car downshifts into first just as I'm coming to a complete halt, there's this dull thud from the back that honestly feels like someone's bumped into me at crawling speed. The first time I actually got out and checked the rear bumper because I was convinced I'd been hit. It's a 2014 A8 with the ZF 8 speed and I've read that these are generally pretty stout gearboxes so I'm hoping it's a mount or a bushing that's worn out rather than something catastrophic inside the transmission itself. The gearbox otherwise shifts beautifully through all eight gears, no slipping or flaring, it's literally just that final downshift to first when coming to a stop that occasionally produces the thud. My usual mechanic took a quick look underneath and said the rear diff mount looks a bit tired but he didn't seem convinced that alone would cause such a pronounced thump. I'm trying to decide whether to start with replacing mounts and see if that cures it, or go straight to a proper Audi transmission repair specialist for a full diagnosis before I start throwing parts at the problem. Anyone else had that rear end bump sensation on their A8 or A6 and what did it actually turn out to be?