I think what would help the most is to STOP sewing for a while, get some rest and come back with a refreshed mind. After some rest, you might see the problem right away. I have learned the hard way, if I am tired it is soooo much easier to make mistakes. Good Luck!

[QUOTE=LoupEsprit;5732354]
Am I just super tired (which I am) and missing something obvious? Or is there something odd going on here??[QUOTE]

If I get real tired I ALWAYS forget to lower the presser foot handle, and that will create the loose bobbin thread.Here is hoping you find out what is wrong. Merry Christmas all!!!
:D

I would never have thought of it, but someone told me to spray the canned air--you use on your computer, ect,into the bobbin area to remove lint and dust. It works really great, and can collect more there than we can see.
Don't use it for very long, or very often. There is water in it, and can rust the parts if used a lot. Once in awhile it is a life saver--like every 10 days or so.
Mariah.

A technician once told my friend that your machine is only as good as the thread you use!

Also check to see if your needle holder screw has come loose enough to let the needle drop down a fraction--that was my problem. Also when changing needles, be sure it is all the way in where it should be--that was my problem. Sometimes, you just have to shut the machine off for a few minutes and let both of you cool off !!!! Ask me how I know!!!!!!!!!!

with all the suggestions about thread, remember to cut your thread at the spool and draw the cut thread thru' the machine and out the needle. DO NOT pull the thread back up thru' the machine to rewind on the spool. Causes lots of lint.

When i have this problem, it generally means that when i put the bobbin area back together, i didn't make sure the cutter bar on the thread cutter was all the way over to the left which means there is a bit of a hook on the right side that is supposed to engage with the bobbin case holder that keeps snagging when you are sewing which throws the timing off so the needle ends up not engaging bobbin thread right. i found this out after rethreading etc as noted in above posts. i suspect that sometimes when i've done all of the above i have ended up pushing the thread cutter bar back and just never knew it. Now i look for that first.

LoupEsprit first when thing start going wrong like this to me i am normaly real tired and need to walk away or go to bed. It sounds like something went went wrong with your top thread. I was told that one of the rules of sewing is " if the stitch is not right on top something is wrong with the bobbin, and if the stitch is not good on the bottom it is the top thread. First thing is rethread the top because you are having trouble with tangling in the bobbin area. the thud may have been your needle trying to get through the bunched up thread. I have a machine that in the middle of me sewing something one of my top tennision guides will come undone, do not know why it jus does.

However because you have adjusted your tensions and missed with the bobbin you may have more of a problem now. I readjusted my bobbin one time and really missed things up had to take it in. happy quilting yippie

Change the needle-99% of the time that type of problem is a needle that has gotten dull, bent or has a burr.

I haven't visited here for a long time, but yippie is right--if there is a problem on the underside of the fabric, it is the threading from the top that is a problem. Problem on the topside, it is the bobbin threading.