Attitude indicator oscillation

[SuperCub]

I always had some difficulty to adjust my A/P pitch channel. The A/P always was hunting the altitude. Now when I watch the attitude indication it is oscillating in pitch and I believe the A/P is just following these oscillations.
Question is how is the attitude indication calculated? What could cause these oscillations? Which data inputs are used for the attitude?
After I exchanged the heated pitot tube per the S/B I have the feeling it is slightly worse.

 

[dynonsupport]

Attitude inputs include:
* GPS (used only when airspeed from pitot and static is not available)
* Pitot
* Static
* Rate Sensors
* Accelerometers

If attitude is oscillating in stable flight, there may be a failing sensor in your unit (if you have a EFIS-D6/D10A/D60/D100 or FlightDEK-D180) on the SV-ADAHRS-200/201 (if you have a SkyView). Another possibility is that excessive vibration may be influencing the display of attitude. There is a warning for this in SkyView, but not in our EFIS/FlightDEK products.

If you have a SkyView, we can have you send us a Dynon Diagnostic File - please contact Tech Support - 425-402-0433 or support AT dynonavioncs DOT com for the procedure.

I always had some difficulty to adjust my A/P pitch channel. The A/P always was hunting the altitude. Now when I watch the attitude indication it is oscillating in pitch and I believe the A/P is just following these oscillations.
Question is how is the attitude indication calculated? What could cause these oscillations? Which data inputs are used for the attitude?
After I exchanged the heated pitot tube per the S/B I have the feeling it is slightly worse.