Originally Posted by WhitsQuilts
If that is the bottom of your quilt, your top thread tension is too loose. The good thing is that the unstitching is easy!
That's what I would say. Right now I am in a quilting class (8 weeks) to learn the finer aspects of quilting. We use the Machine Quilting Made Easy by Maurine Noble
http://www.amazon.com/Machine-Quilti.../dp/1564770745
One of the first exercises she has you do is test the tension of your machine. You take a sample sandwich and mark lines horizontally at 1" increments. Then you start at line 1 and set your tension to 1. Select your stitch and sew at that tension until you get to line 2. Change the tension to 2 and sew to line 3. and so on. This REALLy helps understanding your machine and finding out at which settings she sews best.
You can try this method using different stitches, different threads, different battings, etc. Takes the fear out of the tension issue.
Good luck.