Could be CV joints - when they lose their grease and get dry, they clink as the steel balls move in the joint. On fronts this usually occurs when turning, but there is the same sort of joint right at the front of the rear diff that is known to make this clink noise. Normally this occurs when moving from forward to reverse but in a manual car it could also happen when the clutch loads and unloads the driveline, especially in low gears when the torque is higher...

*edit* - the joint looks like this...

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)