I can handle the "bird's nest" that my Janome 6600 makes on the back of my quilts when using the locking stitch...but, I noticed the bobbin thread is showing in the front of the quilt's stitching. I just thoroughly cleaned her before I started quilting the last baby quilt...any suggestions. I have never touched the bobbin tension in the 4-5 yrs I've owned her.

If the bobbin thread is showing on top then the top tension is too tight. At least that's what I've always thought.
Are you using a different thread or fabric weight than before? If so, you may need to adjust it a bit

You can start with a starter piece of fabric and then the nest will be on that and not the quilt.

I always recommend to use the same thread, specially the same color on the top and bottom. You can adjust your machine to have the perfect tension for that particular thread or fabric or sandwich in general, but even the best machine hiccups every once in a while and your bobbin thread will show a bit. If you are using the same color in the bobbin, you will not even notice. I always prepare a practice little sandwich to make sure there are no bird nests in the bottom. Sometimes we try to match the top to the top and the bottom to the color of the bottom fabric, but I prefer to make sure that my top looks good. After all, that is the part you see first and most of the time. I tend to make wallhangings a lot, and I don't really care about matching the color on the back.

Quiltville has a tutorial on using the starter pieces to make a whole quilt. I have quite a collection of starter blocks to use "someday". Using the starter sure saves lot of frustration.

I LOVE Quiltville' method,

agree with checking your thread colors, etc. you may now be using a different batting than you have before ? I always loosen my top tension some when I am quilting (not piecing).
always test on a sandwich of what you are doing. good luck !

when you cleaned it did you give it a new needle too? you'd be amazed the difference that can make, also, if a piece of lint gets caught in the tension disks it can make it (suddenly) seem like the tension is off.