Bought an mk3 octavia 4x4 a year ago and after changing to summer tyres the car would not drive in a straight line at higher speed, but drifting from side to side in a pendular motion, causing it to almost drive slalom. Had 4 wheel alignment and it was way off, but even having this corrected twice it did not fix the problem. 

 

Driving at roads with deep tracks is scary. Feel like it will drive off the road. On new tarmac i dont notice it so much. Back on winter tyres again and its barely noticeable. 

 

The garage has checked for looseness at all wheels and cant find anything wrong. Any suggestions folks? 

Probably tram lining, what size wheels and tyres do you have?

Its 185/65, belive its r16. Same on winter and summer tyres. Both continental.

205/55 is the normal 16 size I think. Those tyres are are particularly narrow for a car like this. What pressure are you running them and have you checked the rotation direction?