Gyro Rate Bias Issue

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Using the ADW22307 Gyro (dual use gyro/accelerometer board), there tends to be a little rate bias. The result is that, when the gyro is kept still, the reported heading (getAngle()) tends to creep in the same direction over time.

As a point of reference, I've noticed that after 5-6 minutes the gyro reports an error in excess of 90 degrees. This is a bit concerning to me, even for a 2 minute match where we're planning to use MecanumDrive field frame.
Does anyone know why this would be happening, and what can be done about it? The FRC Java Gyro method doesn't allow a bias to be set, and using the reset() command can interfere with driving capability (you'd need to ensure the robot is pointing away from you to get a good reset)