Some models like my Gibson SG and Epiphone have a screw at the end of the knob. Try tightening it a little, that will stiffen the mechanism a little and it can help. Worked for me
@michael_41: Thanks mate, I hope you like it! And, just so you know, when you hover over someone else's post, there's that thing, 'Multi-quote' that comes up ;)
The good part with cheap guitar is that they are wonderful learning tools. You have a good occasion to learn how to set it up yourself without risking to damage a 500$ guitar. I know many players who succeded at their first try plus you get the satisfaction of having done it yourself. There are many sites that will provide you with simple guidelines as to how and what to do. There may even be some posts regarding this in here, there was one on SA but I'm not familiar with the site here. In any case, Google is your best friend.