Interesting thread... I have a S2 with a similar problem... only when engine running, and only at idle, about every 5-10 seconds, coming from somewhere behind the steering wheel/under the bonnet maybe I hear a dull 'clunk' like a mechanical switch sound. It's really weird. I thought maybe low fluid level in ATTESA reservoir?
I have seen my 4WD light come on once. I pulled over & turned ignition off, then started it again and it went out & haven't seen it since...