Steering shake at over 65mph

[omodos]

Hello to all, not that i am in the habit of doing this but i briefly let go of the steering wheel whilst doing 65mph and over on a straight stretch on the highway... the steering wobbles slightly, its not to the extent where i would have felt it whilst holding the steering wheel, nevertheless it bugs me,had an alignment done recently after rear bush and suspension work...and also had one tire at rear replaced after all this...you think it needed aligning again after rear tire changed? Make matters cloudier no idea if steering tremor was there even after alignmignent was done initially, just concerned the trembling will eat through my tires quickly........any feedback much apreciated