Fortunately I'm entitled to a 30 day bumper-to-bumper warranty... i
noticed a small oil leak undernear the Explorer in my driveway so I
made an appointment. Verdict on the oil leak was a broken seal which
they replaced, and the rattle was a loose heat shield (as I first
suspected).

If the problem comes back I'll keep everyone apprised. Despite these
two minor problems I'm very happy with my purchase. My friend who
bought a new 4Runner last year for roughly 4x the price is fairly sour
right now since my 4-year used drives like new and I'm paying far less
in insurance.