How do I tell piston slap, lifter tick, and rod knock apart on an LS I am thinking of buying?

Listen for where it comes from and when it changes:

	Lifter tick	Rod knock	Piston slap
Sounds like	Light, fast tapping	Deep, heavy knock or clunk	Hollow rattle/knock
Where	Top of the engine (valve covers)	Low in the block / oil pan	Cylinder walls
Cold vs warm	Often loudest on a cold start, fades as oil pressure comes up	Doesn't change much with temperature	Loudest cold, often fades as the engine warms
Under load	Mostly steady with rpm	Gets louder under load and acceleration	Most noticeable at idle and low rpm
Seriousness	A warning — fixable if caught early	Major engine work	Wear or piston damage

Quick checks while it's running:

• Use a long screwdriver as a stethoscope: tip on the valve cover, then on the block, handle to your ear.
• Watch the oil pressure gauge — a rod knock from a worn bearing usually comes with low pressure.
• If you can, disable one cylinder at a time (unplug a coil). If the knock drops away on one cylinder, that rod bearing is the likely culprit.
• Rule out an exhaust leak, which can sound like a tick: look for black soot around the exhaust ports.

Buying advice: a confirmed rod knock means you're buying a rebuild — price it that way.