I agree with Micron. Also, regarding your tone problems: if you have just recently started giving close scrutiny to your tone, you will likely find some big fluctuations. It isn't that they weren't there before, it's just that you didn't notice them before. It will get better with all that close attention. You're just training your ears better.

You should observe closely when this thing starts to happen. My opinion is that as soon as you notice it you try a complete relaxation of all muscles on your face. Yes... including those around your eyes. Go back playing again and try to note the difference.
Sound silly, but it works for me after hours of playing...

Zevang