Leaf spring noise on 2003 F53. Anyone been through this?

Ours only has 15,000 miles on it, 3000 of which we've put on. There's been a "clonk" from the left front suspension all the time we've owned the rig. The original owner, from whom we bought it, said it had been there from new, nobody could find what causes it, so just ignore it.

As an engineer, it bugs me a little, but I decided to follow the advice.