"TIm Gilbert" wrote:
We've considered having the prop balanced but figure that if it
was a prop problem it would occur all the time.

No. An imbalance will be more noticeable at particular rpm, especially
higher rpm. You should have the prop balanced statically *and*
dynamically. If this has never been done, or not done in a long time,
you will probably notice a big difference, even if your immediate
problem has some other cause.
--
Dan
C172RG at BFM