I have 2004 F150 w/5.4 engine w/24,600 miles. Whenever I start it, it sounds rattling briefly, like there is no oil where it needs to be. Would synthetic oil or the additive ER or something else solve this?

Depends on sound really? Are you running FORD oil filter? What weight oil? You can try the additive if that doesn't work try running thicker oil could be lifter bleeding out overnight.

sounds like the lifters are pumping back up from sitting over night, give your ford service tech a call, i'm thinking this may be normal
you're probably using 5W-30 oil, it's what's recommended in my '97 expedition with the 5.4 triton motor
hth
Rick, Ore

sounds like the lifters are pumping back up from sitting over night, give your ford service tech a call, i'm thinking this may be normal
you're probably using 5W-30 oil, it's what's recommended in my '97 expedition with the 5.4 triton motor
hth
Rick, Ore
Not normal. But Rick does bring up a good point these particular engines the new 3V 5.4L do have noise that s considered "normal". FORD did put out a few TSB s that addressed engine noises. One for the VCT(variable cam timing)sprocket(if a 4.6 this does not apply to your engine) and one that said to use motorcraft oil filters only. Lifters i have done my share of on the new 5.4 if you get under the truck you'll hear a clicking noise mostly by the exhaust manifold.