I'd make sure every thing that is supposed to be lubricated on a regular basis is up to date. Get in touch with your senses as to where the sound and vibration is loudest. Does it do it only when the blade slows down, does it only do it when the engine is in neutral and it is turned off, etc..
Took the blade off and it balanced perfectly, however, the nut that goes on started to turn round and round. Have to get a new nut, but used thread lock on it and it is holding ok..no more shut down noise.