Originally Posted by beer_truck
I have a 2010 4.6l F150 with 43,000 kms. No mods or after market items on this truck. I run synthetic oil and change it at 12,000km. Last week I was on the highway at approx 100kph/60mph and I heard a rattle, I released the gas and rattle left. This has repeated many times since. OK, everyone will think this is spark knock but it happens on the flat, I never have a problem on hills or when I am loading the engine. I did put gas line antifreeze (in case I had water in the fuel) and refilled with high octane. I am still having this issue. It sounds like it is coming from the engine but hard to get out a highway speed to have a good listen. I'm not sure if maybe I am getting a noise from the transmission or elsewhere? Truck seems responsive and no vibration and except an occasional rattle.
I haven't taken it to the garage yet. I search various forums here but only found spark knock which my symptoms don't fully match. I have not put any fuel injector cleaner since I purchased it, however that is my next tic on my list.
I'd like to look into this for you; please PM me your VIN so that I may do so. Meanwhile, I encourage you to take an appointment with your dealer to make sure everything is OK.