OK, try the tension then, different fabrics and battings have different results. I used to be afraid to adjust my tension, but not anymore. If you adjust your top tension, you may have to adjust your bobbin as well. Stitch on a practice piece as your adjusting your tension.
Ive learned alot from Bob @ Superior Threads, what needles to use with what types of thread and tension etc.... here is a link to a Thread Guide that is awesome. I have printed it out and placed it on the wall by my machines.
http://www.superiorthreads.com/media...HOME_10-10.pdf