I've been feeling like my bike steering has been a little wierd, so just as an experiment when I was going about 12mph on a straightaway, I let the handlebars go to see what the bike would do. Instead of going straight, the bike (on its own) turned right, then once it moved right a bit, it turned back left, then back right... almost like a really slow tankslapper. The handlebars didn't go all the way left or right, but it was a wierd sensation as I naturally expected the bike to go dead straight when I let go of the bars. Should this happen? Or do I need to get a professional alignment done.