He may have a hyperactive thyroid. Have him vet checked.
Gail
"davout" wrote in message
om...
Our cat is 17 years old and is in reasonable health for his age.

However, about a six months ago he started to emit this very deep
moaning cry, almost a growl.

He usually starts this when he comes through the cat flap back into
the house, or perhaps in the middle of the night when nobody is
around.

Is this usual? Any ideas what this might mean?