2000 Lincoln LS Engine Ping or knock

I have a 2000 Lincoln lS 3.0L 5 speed with 140K. I have no engine codes but when the engine is up to temperature I get a wicked pinging between 1K-3K RPM. I use only 93 octane and have tried fuel from different places but nothing helps. When I get on the throttle under load the pinging goes away and at idle there is no noticeable pinging. It's really when I'm at low-medium throttle that it's embarrassing when driving around town.

Any ideas?