Thread loops on bottom of fabric


I started seeing small loops on the bottom side of my fabric.  I have changed the following with no luck: thread, bobbin, needle, and bobbin holder. I have thoroughly cleaned my machine.  I have checked the area under the bobbin holder for any nicks or scratches. I have been able to determine this problem is not showing up when I change the speed on my machine to the medium setting.  Is there anything I can do short of taking it in?  It's last maintenance was about 7 or 8 months ago.  I'm attaching pictures.  Thank you in advance for your assistance. 

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