Aerial = common problem... the plastic internals break easily over time. New generic powered aerial is about 20quid from Maplins and easy enough to fit.
Diesel noise = variator as you guessed. To change it, you need to do the belts at the same time. It doesnt damage the car so if you dont mind the noise, live with it until you need the belts doing. A new variator is about 90quid IIRC.
Squeak = could be all manner of things from a sticky brake caliper to a knackered sub-frame. Get a specialist to look at is ASAP, as if its the sub-frame it needs to repaired sooner rather than later.
-1998 916 Spider 2.0TS Lusso-
H&S Corse stage 1.
CATCAMs stage 1 cams with Savali custom ECU remap.
305mm discs with 166 4-pot callipers.
Ragazzon exhaust mid section.
Biscione Racing 2x70mm rear section.
17" Zender Siena wheels with 3mm rear spacers.
etc etc etc!