I have no idea but it surely could be a possibility especially when the gears are under load. I am utterly amazed at the automotive industry where they can generate power in the first place and then transmit it with a whisper of noise....unless you have a BMW, Lexus or Mercedes.
A bent shaft is easy to detect if you have access to it. I would think that it would take a pretty good out of round to cause any noticeable racket, over and above what would be coming from it in OEM condition. A worn support bushing just in front of the prop could give you a growl I would think. That too should be easy to check if you have access. Bad gears in the V drive I think would whine; however a bad ball/roller bearing supporting the drive shafts would growl. Water in the gearbox with the boat sitting idle for a period of time could do that for you. Since oil floats, the lower bearings would be the most suspect.
HTH,
Mark
