knocking sound (or pinging) is very hard to describe.
if you can hear a metalic sound or if it sounds like "shaking a can of sand/marbles" or a rattling sound ...when u accelerate your engine, then your engine is knocking.
Anyone can give opinion on 3 Garrett turbo series, Garrett GT 28R, GT28RS aka Disco Potato and Garrett GT30R. Anyone have real life advise on those and how much those turbo cost in the market?