I realize this is an old thread but so much useful tidbits!

I sew "everything" on my 15-91. It will get noisier if the needle is dull. So will the feather weight (and I'm sure others as well). It will literally be a hammering noise. I was told of a lady who had never changed her needle in 30 plus years going into a quilt shop an asking to buy "a needle". The lady telling me this story said she about sat down!

I tried several "hopping" feet and hated them all for FM. I have my dogs up (or slightly up- depending) and a light down pressure on the pressure foot. I use an open toe foot. I tried the hopping foot hack by Leah Day and still found I liked my open toe foot better.

The thing about the 15-91 is the bobbin side is as nice to look at as the top side. I actually like it appearance -wise over the longarm bobbin side!

It could do all kinds of strange things if you use a wrong bobbin. Make sure you are using a 15 bobbin.