Welcome aboard. I hope you love the quiltingboard as much as I do.
I support all of the above posts.
Are you using a different weight of material for your backing?
If it is a light weight backing and you have the height and weight of the batting and topside fabric between it and the pressure foot, the feeddogs may be working faster or slower than the needle. Veterans, did I get that right?
I think a quilting foot stabilizes that situation but I have never used one so I don't know for sure.
Can you make a sandwich from scraps to do test runs on?
Make a run with just top and bottom fabric. Bunching?
Add batting and make a run. Bunching?
Drop the feed dogs and make a run. Bunching?
Adhese or pin at 3 or 4 inch intervals and make a run.
If it is still bunching:
Flip the lining to the topside and repeat the test strips above. Does it still bunch? On the needle side or the feeddog side and on which test run did it start to bunch?
If it is still bunching after all the test strip you may have to adjust your tension for this one project. I need the veterans to coach you on that so please let us know if it gets down to that.