Followup regarding my hum problems with the E5 first reported in
this post (see there for details).
I ordered a new unit from head-direct. It does not have the hum problem, so it was definitely a bad unit (how rare we don't know, I think kpsalm was the only other forum member to notice/report the same problem).
I'm returning the old unit for a refund (I did this rather than a straight exchange, b/c I didn't want to be w/out a headphone amplifier while the exchange was happening).
Thanks to everyone who checked their E5's. If anyone else comes across the same problem - maybe the FiiO rep will take notice instead of blaming the problem on line noise.
BTW - both orders from head-direct were processed same day, and arrived in 2 or 3 days from NY to CA via first class mail - $24 including shipping.