I'm only a beginner at FMQ, but there are two things you can try. One is adjusting your top tension, very slowly at a time. The other thing is to change your needle to another size, depending of the weight of your top thread.
The other day, I tried a heavier top thread and turned up with those nasty bobbin loops, and changing the needle to a larger size stopped it. There are many places where you can read about which size to use with which thread. This is one of them:
http://quiltbug.com/Articles/threads.htm