I drive my (explorer swapped 5.0) Bronco nearly everyday and it started making a flutter sound (not ticking) coming home. It only happens during moderate to heavy acceleration. Maintaining a speed doesn't seem to recreate the sound. No engine light. I checked the headers and I didn't see any exhaust residue (yet) and the bolts were still tight. The only thing that changed were adding a 1/2 quart of oil (it was a little low).
Any ideas where to start?