Info needed: Strange Sound

[Wayne Hingley]

Phil, that is indeed a strange noise. Sounds like someone knocking on the door wanting to go for a ride with you.

It sounds something like "water hammer", could it be some type of "thermal expansion" that occurs for a couple of seconds as things warm up? Im thinking something like an exhaust hanger, exhaust pipe, or something like that?? It happens about 40 seconds after the engine is running, so the gasses would just be starting to get hot and transferring energy into the surrounding metal.

It would be good to do another cold start when you are in position and able to get under the truck and observe/listen closely.

Good luck!