94' Yamaha 150 Saltwater Series. Every time it is put in gear there is a knock in lower unit. At idle in gear the knocking is constant until throttle is engaged. With engine off and in gear there is a lot of play in prop and you can hear the knock when wiggling prop back n forth. Otherwise there is no noise to indicate a bearing is going bad. How much play is ok? Is this a characteristic of a bad clutch? Or could shift cable be out of adjustment? Or Rebuild needed? 
