sewing parts on line says you need a class 15 METAL bobbin for a quantum 9920...here's the link...
http://www.sewingpartsonline.com/Sin...ine-parts.aspx
you could call them and ask just to be sure..I was not aware that Singer was putting metal bobbins in any of their new machines.
as far as your birds nests..I have a fairly new Singer Perfect Finish...I oil it and clean the bobbin case before every bobbin change..but yet..all of the sudden I was getting birds nests and skipped stitches like crazy..finally, I took the bottom off of the machine, (originally I thought I had to time it)..well it was just full of lint underneath the bobbin area, where you can't get to or see without taking the bottom cover off! I cleaned it and oiled it, and it is sewing like a dream again. It doesn't take much to throw these newer machines out of whack!
I also agree with the other poster that said it is definately a techniciam problem..there is no excuse for returning a machine to you that still gets birds nests!