Knocks on Start-Up But Only Lasts A Few Seconds

^ Improper oil viscosity. Change oil and filter. Fill with proper oil type and viscosity for expected operating conditions.
^ Excessive piston to bore clearance.
^ Excessive piston pin to piston clearance.
^ Excessive crankshaft end clearance.
^ Excessive crankshaft bearing clearance.

NOTE: Some engine noise may be normal for 1-3 seconds at start-up. Be sure that any noise that is identified is really coming from the engine. (i.e. ABS initialization noise)