I' m hoping that someone may have an ideas as to what this could be. I have a 2004 F150 xlt with a 5.4L v8. Recently on two occasions in the past month as I've left for work the truck would make a rattling that I could only compare to the sound of a muffler dragging. This sound would only occur as I would accelerate. I thought the fan may have been hitting something but it appears clear. I then thought that the motor mounts may be failing and that the fan was hitting something only when the motor revved. After reading numerous posts, I thought perhaps it may have to do with a vacuum leak and the 4wd. I switched to 4x4 high when I last heard the sound, but nothing changed. The only work to have happen to the truck in the last several months was recently having the starter replaced. One last oddity: if I restart the truck a couple of time, the truck drives with not a sound regardless of what it is doing. As I was writing this I just started wondering if the starter did not retract 100%, could the meshing gears make that sound as it accelerates? Any help would be greatly appreciated. Thanks!

 

Yes a improperly acting starter certainly could be what is happening. Considering that was what was done recently.

What would help us here more, is, what year of truck you have and how many mile are on it and the engine size???

 

well sorry, I did not see earlier the 04' & 5.4.
and just another passing thought was a heat shield over the muffler. Well, more of a heavy self adhesive foil pad, at least on my 02' there was one. Anyway the adhesive gives up over time & a corner can fall on the driver shaft making a grinding noise too.

 

Thanks Enriched.
I had thought of the heat shield. The rattle does sounds very similar, but it wouldn't explain why it only occurs after a start up. If it doesn't make the noise from start up, it won't make it for the entire time that the engine is running. As for the millage, the truck is right around 85k.
Any further ideas are greatly welcomed.
Thanks,

 

considering that it is a 04' that brings more questions, is it a Heritage edition?? Heritage editions still ran a 2 valve engine (2v)still got the old style, ..regular 04' got the updated 3 valve (3v) engine/heads, more of a head update..

If you have a 3v engine...then you might have a cam "phaser issue" which is pretty involved

 

Thanks enriched.
I think it was the starter.
Removed the rebuilt duralast starter and found that the bendix spring was not full retracting the gear. Installed another starter (brand new instead of rebuilt) and haven't had the noise return yet. Fingers crossed I won't hear it again. Thanks for your help.