So I've leapt from a crappy clio (best move ever) to the vrs with big 18” wheels. I notice cruising on motorways the road noise is quite a lot louder (if you discount the clio engine struggling to keep 70 on the speedo)

I have knocked it out of gear and so I guess it is not transmission. It isn't whining etc, it is a low rumbling that sounds like it is each wheel.

Do big fat 18” tyres make an audible sound cruising? I have owned enough dodgy cars to be confident it is not a bad sound, just wondering.....

Road noise in the Octavia has been a constant criticism in reviews for a while now - hopefully it will be less in the new model.

I turn the radio volume up!

To be fair, coming from a crappy clio, I cannot criticise any aspect of this car.

If your wheel alignment is not spot on (especially the rear) it can effect the road noise. There is a bulletin from Skoda that covers road noise and excessive wear on the tyres. Do a search on here s there are many threads about such a topic.

My last two VRs's have had to have 4 wheel alignment due to this.

Don't think it's an issue. The tyres have done well over 7k miles and look as good as the day they went on with no unusual wear. Dodgy tracking would start to show by now wouldn't it? Just wondered if big fat 18's made more noise than clio tyres? Logic would say yes, as there is far more road contact area.

I also notice an audible swooshing noise from the wing on the back at 70+

Just another characteristic of an amazing car I guess....

Its a characteristic of the car not the tyres or tyre size as I run an Astra H too with same brand and size tyre and its massively quieter than my VRS. My VRS was no quieter after alignment I had done recent too. Sound deadening session happening with the warmer weather coming. Priced everything up at about £150 and that includes pads for inside wheel arches (waterproof). The main culprit seems to be boot floor and under rear seats that generates the noise which is deflected off the back window into the cabin.

http://www.carinsulation.co.uk for the bits

It is a well documented Octavia II feature through many threads on here. Some tyres are better than others and having owned/driven Octavia II's with 15", 16" and 17" wheels I can say that the bigger the wheels the worse it is. It also get significantly worse as the tyres wear so beware the many "I put on XYZ tyres and the noise went away" statements.

I had 4 wheel alignment done on my current car at around 12k miles. The reason wasn't noise but the steering wheel hadn't been straight from new and the dealer insisted they couldn't do anything without risking throwing out the tracking(!) As found, the rear wheels were all in spec but at different values. They were adjusted to be identical. Over the miles the droning and vibration developed until at 24k miles the rear Bridgestones were badly sawtoothed and the noise was unbearable, especially at 25-35mph and 60-70mph.

"I put on 4 Michelin Primacy 3's and the noise went away" - like driving on carpet! Miles will tell if the noise returns but 3k on they are still very quiet.