The sound you are likely hearing is most probably attributed to a friction noise, a sound resulting from the massage heads sticking to the casing.
This can be easily addressed by opening the casing and applying a lubricant to the white fabric surface. Doing so will effectively reduce friction and eliminate the noise.
You may use substances like candle wax or even gently rub with some solid soap for this purpose. Your device should operate more quietly and smoothly after following these steps.
If you encounter any challenges, feel free to reach out for further assistance.