Tramlining Tyres issue?

[94 325 0]

I now have a 2004 325Ci MSport with factory 17" alloys. I have just replaced the factory fitted Michelin Pilot Sport REAR tyres (for Dunlop SP Sport Maxx) and left the Michelin's on the front (as there is still good tread there). Now the car handles completly different, steering seems to be eratic and I am correcting it all the time: - Tramlining I believe is the problem. Was 'perfect' before fitting the 2 new tyres, now not afterwards. So, I am trying to get hold of new Sport Maxx tyres for the front (Dunlop NZ don't actually have any for a couple of weeks) - so atleast I will have 4 new tyres all the same brand. Rears are 245x40 fronts are 225x45. Will the new fronts fix the 'problem'? Is this common when having different brand tyres front/rear?? Any comment would be appreciated, thanks.