I love my Brother SQ9000. It was a very recent gift from my husband. When I started to quilt, about 4 months ago, he said that he thought an electric machiine would be better for me and "It was on sale". I love the machine. I too have the clunking noise once in a while. It only occurs when I stitch in the ditch or go through too many layers. A sharper needle sometimes helps, but not often. I guess we will just have to get used to the noise.
PS: I do have other electric machines. A singer that was my mothers (circa 1949), a kenmore (Sears) from 1980, a "mini-Singer". That is a toy sewing machine from 1954. It was a Christmas gift. It is what I learned to sew on. And of course my non-electric machine is a singer treadle machine from 1889. It works great and I use it for any large sewing.