is he the ferret with regurgitation and now these noises?  Is it easier
to eat when the ferret is held very vertical with the head much higher?
Have you and your vet considered megaesophagus as a possibility of so?
See:
http://www.miamiferret.org/fhc and use the easy search engine there.
 
Does it sound similar?
 
There are several megaE articles in there to help find, understand, and
provide care.
[Posted in FML issue 4126]