during acceleration between 40-50 I hear a knocking noise very light but you can make it out. Told 3 local Ford dealerships and only 2 out of the 3 said for was aware of the problem. One dealership said it was fuel related? but didn't offer to change fuel filters out to see if there might be water in the system. I know on my 18 wheeler when you this kind of noise my mechanics generly do an uphead job (tighten lifters and so on) and that cures the problem. so my dealership just noted my account and if theres a problem it is noted.