Many have been diagnosed as timing chain because it does sound like that.
When you hear it, look real close at the top bushing and you may notice the shock moving back and forth on the mount .
[ sideways] . And as you have noticed, it does this mostly at idle , in gear.
. The side of the shock eye is hitting the washer on the mounting bolt. If this is the problem, it can be fixed by
inserting a thin rubber washer/o-ring between the washer and shock.
But if the wear is excessive, replace the shock.