Rattle at startup like you described (especially after sitting a while), sounds like the issue with the front cassette tensioner. There was a TSB, which had you replace the front tensioner (which is external, screws into the head) with a new one with an oil resevoir built into it, and at the same time you rmeove this little plug next to the tensioner to insert this little plastic 'anti-drainback' thingy. The idea is that after sitting, and oil drained back into the pan, during the time it takes oil pressure to reach the head, and provide 'spring' to the tensioner, the front chain makes a lot of noise until pressure builds up and full tension is restored (I understand these tensioners are kinda like valve lifters, oil pressure provides some of their 'spring').
the problem is, to get to that tensioner to screw it off, and that little plug, you have to remove the lower intake manifold, which is time consuming, so Ford combined this TSB with anther one they were going to come out with (two birds, one TSB), which replaced the leaking o-rings which the intake uses as gaskets. It may be possible to replace the tensioner and plug without removing the intake, something to look into.
If you are also hearing a noise between 2K-3K rpm's that sounds surprisingly like ping, that would the jackshaft timing chain (the tensioner goes bad, so chain is all slack). There are 3 chains to drive the two cams, the 'jackshaft' chain, which is in the position of a traditional OHV timing chain (the normal 'cam' shaft is replaced with with this 'jackshaft'). The jackshaft then drives the two chains to the real cams above the heads, one at the front of the block, one at the back. The front one drives the drivers side cam, back is passenger side cam (refering to RHD countries, of course).
To do the jackshaft tensioner you have to take the front timing cover off, not a small job, and since yo are going to want to replace the chain and sprockets (and consider the front cassette (drivers side cam chain) as well), you need the special tools that hold the cams in place (since there are no timing marks and the sprockets are held in alignment on the cams only with the clamping force of their mounting bolts, so once you loosen the bolts without the tools in place, you're in trouble). So do your homework before you attempt this repair yourself.
If you do need to replace your jackshaft tensioner, I want your old one, even if its in pieces. See thread
http://www.explorerforum.com/forums/showthread.php?t=220598 for more details.
