JD Z225 mower deck vibration

My mower deck is making unusual sounds during blade engagement. The unit still cuts the grass evening, but there is excessive noise and growing vibration from the blades. They appear to wear normally, but the sound seems like the bearings are worn. Something is out of kilter, but I can't seem to isolate. Anyone else experiencing issues like this. My Z225 has about 300 hours run time on it.

Lift it up, disconnect the belt then spin each blade and pulley.
They should all be quiet.
grab the tips of the blade and try to move them see saw style.
Any movement & you spindle bearings are toast
Pull the belt out hold it between two fingers on the V sides then run along the entire length.
You are feeling for a scallop or polished section.
If you find one the belt is toast