That's a hell of a knock sounds like big end to me,
Got a long screw driver? One trick is hold it on places and move around see where it's loudest with your ear on the other end
Don't need to see a dyno when you see a certain race car struggle to catch a street bg on the straights at megameet to vow for them, but dyno plot would be interesting for that bg!
Ummm??? Current drop? You got anything to support this makes it worse? as a sparky the best thing to do is have less current which is less heat, current = wattage/voltage, so having bigger cable you have a higher voltage (less volt drop) which is more important so therefor you draw less current.