Hi Lau Yan Han
Despite all self-criticism, I can not retrace your results. Neither my measurements nor the measurements of other people show such high amplitudes on the MS5525 as yours do.
e.g. see
Plane 3.8.5beta1 released
Plane 3.8.5beta1 released
Plane 3.8.5beta1 released
Photos from your measurement setup would be helpful. Unfortunately, your logfile contains only airspeed data and no timestamps. So you can not determine frequencies. Was the MS5525 chip stably attached ? The MS5525 is very sensitive to direction of gravitation at very low speed. If you made the chip vibrate with the fan, I could imagine your results.
In contrast to my former assessment, I am no longer sure whether the fluctuations were really caused by noise or rather caused by air vibrations or turbulences on/in/at the pitot tube.
The direct in flight comparison measurements between MS5525 and SDP33 shows synchronous amplitude curve, which speaks against background noise. See Plane 3.8.5beta1 released
The ingenious measuring device from David (@palm369) also shows no significant background noise - neither SDP33 nore 4525DO. See New SDP33 Airspeed Sensor and Ardpuplane
Regards Rolf