I thought it was the fan clutch slipping and free-wheel spinning that's creating this sound but can't really pin it down to this do to I have nobody to rev the engine when it occurs so randomly.

Could I be correct on this conclusion?, how else can I double check this, or could it be something else?, and what might that be?....?

Secondly; there's a noise that sounds like the fan blade hitting the radiator shroud. This has been random as well and I noticed it first time a year ago...very random it be.

I checked the clearances on the fan to shroud as well as looking for any type of damage to these parts and everything seems pristine