[universeman]

Bearings in fan could be dry or going out. Unplug the fans and remove the fan shroud and fans as one unit (four bolts - easier to drop out than to lift out but you have to remove the batwing)

Spin the fans by hand and see if you can see which one is making the noise.

Some all-purpose oil in the oiling hole (on the side of the noisy fan - in the metal casing, hard to find so you may need to remove it from the shroud to oil it) will do wonders if it's just needing lubrication. If not, you can replace the entire unit or just the fan - they're available used on eBay and $$$ from Porsche. Good luck!