I am using a walking foot and still I will get tiny puckers or folds at the cross seams while doing STD. I am using a brother CS600i and a Singer 201. I even found a walking foot for the old Singer that matches the rather narrow feed dogs of the older machine. I have tried changing the pressure on the Singer but there is no pressure to change on the Brother. I just can't think of anything else to do

Are the puckers on the front or the back? If the back it might be the backing is not stretched tight enough when you were sandwiching the quilt. If the puckers are on the front the backing may be too tight. JMT. Others may have other ideas.:)

you need to pin and/or be sure the seams are smooth. the walking foot can't do all the work. You still have to give care to where it is quilting. If there is too much fabric, it should be smoothed out. I use straight pins before the walking foot if there appears to be too much fabric.

I did std on 2 quilts and this happend...it drove me crazy. After that, I decided to only do free motion quilting. I tried different battings, different pressure everything. I know that doesn't help much, but I've gone through that too.

I use safety pins fairly close together. I also use the method where you put pieces of tape all the way around the table to make sure the backing does not have any wrinkles. The puckers are on the front of the quilt. The back is just fine. Some people say you don't need a walking foot but wouldn't that make my problem even worse if I didn't use a walking foot.

My Janome is 1 year old, "Quilt and Decor" model, having the same problem, and there is no pressure adjustment. Very disappointed, because it is for quilting. Contacted the LQS where I bought it, no help. Contacted Janome direct, no help. Have pinned, repinned, basted, re-basted, still the same problem. I guess I will have to be satisfied with free motion. Again, very disappointed, but there is no recourse. If I ever buy another machine,and due to my age, that will never happen, I would insist on trying it out first

I have tried FMQ but I just don't like all of that quilting. I like a little puffiness and besides I still can't get the hang of FMQ. I have trouble getting the speed of the machine and the movement of the fabric in sync so the stitches are somewhat even.

Yes, I know your frustration. My brother CS6000i was also sold as a quilting machine. In fact, it came with the walking foot and the FMQ foot. I am going to keep working on the FMQ method but I will have to make big loops or some large design so I have a little puffiness in my quilting which I like.

If they are tiny, after the quilt is washed, they probably won't show. Someone said they are called "kisses" for the person who receives the quilt. I like that... ;)
I wear gloves when quilting and it helps keep the fabric taut. I also slightly tug the area (gripping both front and back at same time) where I am going quilt to make sure it gets the fabric taut. Hope this helps.
As for walking foot, I wouldn't try it without it. You would definately have puckers then.

try putting tension on the fabric, maybe just a little ahead of the foot so that when the foot pulls the fabric to itself it's taut