'99-'04 style Mustang V6 has light knocking/tapping sound

What is your question?

'99-'04 style Mustang V6 has light knocking/tapping sound in the right side of the engine bay. (facing the engine bay, to your right.) Goes away when warmed up. No clue what's causing it, wanting to buy this car. Owner says it's been doing this since he got it in 2011.

What makes this problem better or worse?

Stops when warmed up.

How long has your 2002 Ford Mustang had this problem?

Years