I am in the middle of a piano topper and all of a sudden the bottom tension (doing FMQ) is a mess! I was quilting along and doing fine, and now the thread keeps bunching up and even coming out of the needle as well (how does it do that?) I have done nothing to the tension at top or bottom. I am using an old kenmore (34 yrs old) and it has been great. I changed the needle, put another bobbin of thread in, cleaned out the bobbin section and top plate, my feed dogs are down, what the heck? It seems to work fine of a swatch of just fabric but not with the quilt out of the blue. Any ideas?