Knocking noise?...Sometimes it's just the simple things, or I just got lucky..I flushed my entire cooling system three times, warming it up between each one..Did it until it got to be clear water..After final drain, New Prestone and good clear water...No more knocking noise..I guess there could have been some junk in the water pump..Don't know, but not complaining either..Figured I share, just in case, Steve
