I've got the same phenomenon, and it's persisted unchanged after a new radiator (done for other reasons). I'm convinced that what happens is the viscous drive degrades a bit over time and no longer waits until the temp's risen much before it engages. It doesn't impair the cooling performance, as the final result is the fan engages *more* than necessary at cooler temperatures, not *less*. I'm betting you notice it especially when the engine isn't fully hot yet, and when the weather isn't too hot, as the drive locks up with increasing heat so the cycling stops and it stays constant-on. BTW, the sound pattern clearly rules out the electric fan(s) as the source.
The fan itself, as far as sound created by the blades in motion, is notably noisy. I've known one 107 owner to switch to a later and quieter fan and DIY the shroud modifications, with a reported reduction in the noise level. I've also seen several posts from folks who replace the belt-driven fan altogether with electrics, which also involves a bit of reengineering. The immediate remedy would be to replace the viscous drive, which is on my list of when-I-get-a-round-tuits.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)