Back from the OPC after getting my rattle examined.
No surprise to hear that it is infact the OPRV. The engineer new immediately from the description I gave, but testing confirmed it.
No corrective work has been carried out on the car for 2 reasons. Firstly, changing the OPRV will only stop the problem for a while until it suffers the same fate. Secondly Porsche are testing a new part. Of course there needs to be some considerable testing to prove that it does infact fix the problem and not go again. It is hoped that the fix will be available soon so having to replace it twice in a short time frame is wasted effort, which I completely agree with.
Once the fix is announced, it is likely that the fix will be applied under a recall.
So i'll wait by the phone for the fixture call.
Incidentally, after cruising about for 2 days in a KN, I was surprised in some respects how good it was. Cruising was so relaxing, pop the car into chillmatic and waft up and down the M40 in armchair style seats that really roasted your behind when set on high. Not trying to find fault with it at all as it was a nice vehicle, but I found 2 things wrong with it. 1) it was far to big, I could have lived in it. It made the drive look like bus stop. 2) The drive wasn't spirited enough, I got a little bored with the cruising aspects. Lots of buttons to play with though to brighten up a journey.