Thump??
Here's a couple of threads on the same subject:
https://www.ford-trucks.com/forums/s...light=%2Bthump
https://www.ford-trucks.com/forums/s...light=%2Bthump
If you use the search feature and look for "Thump" you'll find three full pages of discussion on this. I'm at the point where I get worried if I don't hear it now.
Rick





