The guys said "yes, you need a new serving" and started unwinding the old one from the bow string. Then we all got a surprise. About 1/3 of the strands in the string were broken right below where the knock had been crimped on. Righty-o then.
One new bow string later my bow was back in shooting shape, feeling good, and making its normal noises.
The moral of this story? When your gut tells you something isn't right with a machine you know very well listen.