Hi a little education for those who want to learn, Bavarius tyres are made in the Czech Republic and were originally back in the thirties a subsidiary of Michelin, in 1992 they signed a joint venture agreement with Continental AG [anyone ever hear of them], for the record one of the largest multinational corporations in Europe who produce just about every rubber O.E. part for German/European vehicles and as for Budget they could not be further from that or the Thames as the brand Barum only produce premium mid range to premium upper range tyres, tyres having watched this thread develop I can as a frequent user of the M25 concur with your problem as my car does the same depending on if you are driving on the concrete side of it or the tarmac side, this anomaly is due to the Audis steering set up as this is not to dissimilar to a version of centre hub steering this allows for very sharp and precise handling, the downside is if you drive on the undulating concrete crap thats known as the M25/M1 any largish discrepancy in the road surface drags at the steering, never had this problem with my Mondeos as they all ran Macpherson struts which the shock absorber runs on a ball race top mount so the strut moves with the steering rather than the steering moving around a static shock absorber, as for steering component wear, its highly unlikely as my A6 has now covered over 130,000 hard miles on a multitude of road surfaces and has no wear, when I could get them at a reasonable price I used Barum tyres for a good few years on my cabs and always got good miles and grip and I can vouch 100% for their winter tyres but alas they are now out of my price bracket so use Nexen another budget tyre company thats only been around for about ninety years which would lead you to believe they must be doing something right, just because you have never come across a brand before it won't mean its no good, just look beyond the name to see who owns the production licence.
Steve