Engine Noise

WARNING: This page is about a different car, the 1995 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.

Check for loose or worn drive belts.
Check oil level.
Check valve clearance. See ADJUSTMENTS - 3.0L article.
Check engine compression and engine mechanical condition. Check camshaft and valves.
Check for loose components.
Check for loose spark plugs.
Check for cooling system leaks.
Check exhaust system for leaks.
Check for worn connecting rod bearings, worn main bearings, loose piston pins, or excessive piston to cylinder bore clearance.
Check for detonation (spark knock).