I posted this topic on the forum about two weeks ago and recieved a few responses. I've also spoken with Amy, but so far my problem hasn't been solved.
I've been a machine quilter for 12 years, so I've dealt with tension issues plenty of times. About a month ago, in the middle of a quilt, I started getting random loops on the bottom of the quilt, as though my top thread was too loose, etc. I tried to fix it, like I have hundreds of times over the years. Nothing I've done has fixed this issue. I've adjusted my tension assembly, re-timed, checked for play in the hook shaft collar (there wasn't any), replaced my hook assembly, checked for burrs, etc.
People suggested that it's the thread or bobbins. I've tried switching out bobbins and thread....the change makes no difference. The only thing that helps even a little is cranking my top tension so high the thread nearly breaks. And even then, the random loops remain. Like 15-20 per twin size quilt.
I'm looking for some ideas, preferably from an admin or someone who has dealt with something similar. Like I said, I'm familiar with many of the basic fixes, but this has me stumped and I cannot continue to work on quilts like this.