Could also be the tyres that are contributing to the noise levels. Bridgestones seem to be a favourite tyre for VW to fit to UK performance models, and they’re quite a noisy tyre.
There’s a view over on VWROC.com forum that post-WLTP cars might be fitted with thinner / poorer quality or less sound insulation in order to for VW to get cars WLTP type approved. Possible weight reduction by using less or poorer sound insulation might not contribute much towards weight saving in order to achieve VW’s CO2 and MPG targets, although every little helps. Some VWROC.com members with post-WLTP cars have also commented on their cars being quite noisy, although not all seem to have this issue - perhaps because different people have different levels of hearing sensitivity, so what sounds excessively noisy to one person may sound OK to someone else. There hasn’t been much, of any, discussion on noisy GTI’s over on golfgtiforum.co.uk though.