1989 Cobra on 4.3 liter engine makes a funny noise

[rolmops]

While testing my engine I heard a funny noise coming like something rattling from in or around the outer unit. It sounds like a loose piece of metal banging against something. It is not bothering the engine or lower unit performance (as yet) and when I engage the gear it goes away. For now I will dig up my stethoscope and see If I can more precisely locate the source of this noise What could it be and what should I pull apart?

 

[Mc Tool]

Ooooh ! that sounds expensive . I would start looking at either the motor or the drive unit .