I have a 05 supercrew f-150 fx4 with the 5.4 3v. It has 138,000 miles. I realize there are tons of threads here pertaining to engine knocks and rattles but I'm not too sure if what I am reading is the same problem I am having.

Some kind of knocking/rattling noise has just started in the engine. I had driven it about 20 miles or so, it sit for about an hour and when I started home I noticed this noise everytime I would accelerate. It only occured if I accelerated normally. If I accelerated very slow it doesn't do it at all, or if I accelerate fast it doesn't do it at all. When I got home I noticed I could make it do this noise in park, though not nearly as distinctly as I could by putting the enging under a little load by in gear and holding the brake while acclerating a little. It seems it took a certain amount of rpm in combination with a certain amount of load to invoke the noise. I cranked it up the next morning to see if it would make a difference when cold and it still made the noise, though i wasn't able to reproduce it in the driveway after a minute or two.

Though I have owned 2 other trucks with 5.4s I'm not at all familiar enough with them to diagnose a noise like this. It's not a uniform rattle/knock like a rod knocking or a rocker arm tapping, but slightly erratic.

Any help on this would be greatly appreciated. I can't afford to simply bring it to a shop right now and neither can I afford to keep driving it if it is going to damage the engine by doing so.