Loose Loops on Bottom, How can I fix this? ?

The top thread on my machine leaves loops on the bottom side of the fabric. I have threaded needle with foot up, that helped for about 2 inches of sewing. Then it goes right back to the loops, adjusting the tention withthe tension nob does nothing. I have adjusted the bobbin and made sure everything was threaded correctly. If I hold the top thread slightly as I am sewing I get a nice stitch. What else might I check for this problem?