Starching both backing and top helps a lot with this problem. I starch the backing *heavily* using a 1:1 solution of Sta-Flo and water. It's a good idea to spray starch the top too. If the quilt is already layered, it helps to mist the top with spray starch, let dry (can put a fan on it), and then mist again several times. Starch stabilizes the fabric so it is less likely to stretch while you are sewing.

A walking foot helps too.

You have to be careful not to stretch the fabric. The bunching at intersections occurs when the fabric has been manipulated too much -- especially stretched with the sewing lines. It can help when sewing to lift up the quilt sandwich in front of the needle, so that you are feeding from above the needle. Never push or pull on the quilt sandwich while sewing. If you absolutely have to, then use the spreading technique with the fingers as you near a crossover line; however, this is stretching the top fabric and will result in some fullness in that area. It's preferable to a sewn-in pucker, but still not perfect. Best is to not have any excess fabric in front of the presser foot ever, and feeding from above (and especially starching both sides) helps with this.