......check your bearings.

The front wheel of my Trek 8000 started making pinging noises, esp. when I had some weight on the front end. Checked it for loose spokes, found none.

Really started watching the wheel and found that it would ping when the labels on the rim where at the 6 o clock position.

Pulled the wheel, removed tube and tire and pulled back the rim tape and could find nothing there to cause the pinging.

As I am holding the wheel, I give it a spin and hear a faint noise coming from the hub. Pulled it apart and the bearings were almost dry. Not sure why they would ping at the same place every time, but once I cleaned and reassembled the wheel, she rides silent again.