Originally Posted by TMAllison

On my 99, a collapsed left motor mount manifested as vibration at the serp belt tensioner. That vib can sound like a knock that gets better as the engine warms up.

You can release the tension on the serp belt (remove the spring) and fire up a COLD engine and run it for 30 secs to see if the noise is belt/accessory device related.

To check the motor mounts, use a rubber bushing between floor jack and oil pan and lift the engine ~1/4" and see if the noise/vib disappears. Dont lift more than that or you can damage the hard connections between engine and exhasut, fan/shroud and/or air filter housing.

Also check the bushings at both ends of the damper (shock); sometimes they fail which causes a clicking/knock.