Tractobots, my attempts at field robots

I’ve been using the BNO055 - the same chip as in the tinker, and i’ve found the pitch and roll to wander upward a few degrees - even as high as 8 to 10 degrees while traveling forward. A soon as you stop moving , the numbers return to zero. I have given up using it as I can’t seem to correct the problem.

Has anyone else noticed this?