Air conditioner filters changed?
 
Warmer house temperature?  Have you switch from A/C to heat?  Cooler
temps make odor less noticeable & fuzzies don't mind (my thermostat stays
on 65.  I wear long sleeves year round, lol)
 
Ferrets altering sleeping arrangements and sleeping in a larger 'pile'
rather than 1 or 2 to a sleep spot?
 
A new arrival changes the 'pecking order' so males have a tendency to do
a "long rub" across litter box edges to make sure the newbie knows he's
around.
 
A ferret that's sleeping longer than previously and emitting more than
the usual 'sleepy ferret' smell?  (Often an early insulinoma symptom)
 
Descenting usually isn't a factor, unless the ferrets poofs frequently.
 
Honestly, I'm not a dog person.  but "several" indoor dogs (any breed) to
me are more odiferous than 7 ferrets, unless they are those pampered pups
that have bi-monthly professional groomer appointments.  So I'd think
something in the environment has changed.
 
Food is a possibility.  I've never fed Zupreem or 8in1 so I can't make
any kind of judgment call on that.  Washing bedding once a week should
be ample for 7 ferrets, and baths are virtually unnecessary.
 
Debi Christy
<http://www.ferrets1st.com/>
[Posted in FML issue 5063]