Thank you for the additional details and repro steps.
This actually looks very similar to the following Cinemachine-related listener velocity issue:
In short, the issue appears to be related to the FMOD Studio Listener transform being affected by the Cinemachine-driven camera update during very fast movement.
Could you please try the workaround/testing suggestions from that thread and let me know whether they improve the flickering on your end as well?
Also, could you please confirm which FMOD Studio and FMOD Unity integration versions you are using?
You can find the Unity integration version under:
FMOD → About Integration