For the guy with the true carpet shark!
I noticed this behavior in both of my males, especially the older.  Loki was
a bit more jittery about the outside world than Falkor since he hadn't been
outside of the pet store's pen till he was 4 mths old.  Anyway, I think that
insecurity may play a big part of it as it is all new to him & he will
loosen up as he gets familiar with the territory.  Mine will all (I have 4)
slink from time to time to the extent of sliding forward with their front
legs folded completely back and flat on their chest (they look like an otter
swimming without the water :>).  I especially notice this when I take them
out for walks.  I read somewhere that they have some scent glands in the
neck area and, if that is so, they may be "marking" their way; either as a
guide to follow back home or just to say "I was here".  Also, itchy critters
that they be, it may just feel darn good!  I also notice when I walk all
four of them, that the boys will walk lower to the ground than the girls.
Maybe it's just a guy thing :)
 
I'ld suggest giving him a couple of weeks to get the feel of his turf.  If
you can, socialize him as much as possible & take him out for as many walks
as you can.  This will help to get him used to people & new surroundings.
Also, watch him as he plays or gets to a flat out run.  He will probably
hunch up & do the war dance from time to time in which case I would say you
have nothing to worry about.
 
Good luck & enjoy
Jean & her fuzzie bundle Nikki, Jewell, Loki, & Falkor.
        * a bundle of joy is a bundle of ferrets *
[Posted in FML issue 1809]