how is your quilt sandwich basted? thread? spray? pins? sounds as if it is not held tight enough...and you should be able to see exactly where you are stitching with a walking foot...i've never seen one that blocks your view...what kind of machine do you have?
i would think you need to baste it better-if you are not sure how to do that there are a number of tutorials/videos- just look for (basting your quilt sandwich) when everything is tight you should not get puckers....should ask though...what kind of batting are you using? if you are using a very lofty-polyester batting made for comforters- tying your quilt may be a better route to take...if you are using a regular quilt batt (like warm & natural, hobbs, dream batt, ect.) then it is probably not the problem- not having the backing tight- basted well is probably the problem-