I don't know since when.. but I noticed it's a few weeks ago. especially driving freeway, steering wheel is kind of shaking. I have fixed alignment on oct last year. Is there a problem on tire or?

 

My money is on a bad tire (tread separation) or a badly out of balance tire/wheel. Maybe even loose lug bolts. You can troubleshoot yourself by rotating your tires from front to back. Good luck.

 

...or something as simple as throwing a balance weight. Pretty rare but it does happen. Also, tires have been know to shed rubber on the inside which ***** up and floats around inside the tire creating all sorts of wierd symptoms which can go along with tred seperation or broken cords. I had all four tires on a fairly new car, less than 10K miles, all go bad withing 3 or 4 hundred miles of each other on a long cross country trip once. They were the factory rinds, don't remember what kind they were.

 

And depending on where you live, if there are a lot of pot holes or severe bumps it could also be you alignment. I have hit bumps and thrown an alignment out of whack. of course if bent suspension parts but that is easier than many people think.

But as ammodave and Fly'n Brick have stated its probably an out of balance tire for some reason either weight missing, tread separation, broken cords, etc.