Looks like you got some good advise. Something I thought of was a good cleaning. If you use towels a lot you may have a large build up of lint in you machine and therefore not functioning correctly.
I always wash and dry my towels,and then iron them to make the pile lay down,stabilize with good stabilizer.......give it a try...........Sue
Barb, I do towels (and only towels...). They can be tick or thin, I always hoop them tight (even if this does mark for a few hours), never use back stabilizer but always use front WWS. Make sure you do a background basting stitch as this does help a lot to avoid puckering. The density of your stitches is also very important. Sometime, I have to embroider twice the drawing to have it dense enough not to see the background fabric. Have fun! Pat
May be it is the thread.
Use nr. 70 on bobbin and nr 40 for the upper thread.
I had that problem too.
Maybe the machine needs a repair or another new needle.
Succes!!!!!Gerdien
Barb, I always do towels one of two ways depending on how thick the towel is. I just for a thick towel hoop tear away and spray temp adhesive to stick down the towel, then PIN or baste. Then I put WSS on top and float another sheet of tear away underneath if design is dense at all. So since you have tried all of that, I'd say your tension must have gotten off. Do a design on a scrap towel (monogram an old one for your bathroom)and see if any of the above suggestions work before you mess with the tension. BTW every time I do anything to my tension, I mark where it was with tape and a pen so I can put it right back when it doesn't help.;)