ive watched a few regens happen with my vcds ,most it doesn't affect the drive , but around town it sounds like the air filter is loose/missing,it has that sort of engine sound too it. the last one I had was Wednesday and Thursday,it started just before my journey end, I could hear it,when I stopped the car ,no fan running ,next morning I had a short trip it started again and it stopped when I got home ,then that afternoon it started again around town , so I drove it for 3-4 miles on country roads and it then finished the regen, typical temps are around 700-800, never seen any higher than that,i do use a combination of a cetain booster and a fuel conditioner /pump lubricant , that's probably the reason temps are lower!.