This shaking issue seems to cause much concern, but it is perfectly normal.
Here is some explanation from fanatec,
"Wheel oscillation typically manifests itself as a rapid 'rocking' from side to side, typically when driving at medium to high speed on a straight. In severe cases, the oscillation can be felt while gripping the wheel, and in less severe cases it is only apparent if the wheel is released or held very lightly.
This is NOT a fault, nor is it unique to Fanatec products. It is an inherent characteristic of typical force feedback signal output, and can become more apparent with more powerful wheel bases with low internal resistance, as the rapid response of the motor and its inertia causes an 'overshoot', which is then 'over-corrected', ultimately resulting in a feedback loop. There are many variables that can contribute to oscillation, including the sim software being used, the platform (PC or console), the overall latency, the Tuning Menu settings, the in-game settings, the vehicle and track combo selected, the vehicle setup, and so on."
https://forum.fanatec.com/discussion...el-oscillation
I hope this is helpful.