can having low coolant cause the motor to knock?

 

as in overheating? me tinks so

 

yes, if your car over heats the in coming fuel will detonate before the spark plug sparks, it's called pre-ignition knock

 

Just to clarify, if it HASN'T began to overheat you should worry about that and diagnose your knocking issue elsewhere. If the coolant is low but it doesn't overheat then the knock is probably happening from a vacuum leak, bad fuel, etc.

-Stig