Immediately after installation it was possible to use without problems.
About 3 months after around the step after construction etc.. And the noise is (Backrest was not the cause at that time) Occurrence.
Consult with the shop about 5 months or so.
Because there was a Wound in the OEMPillion Bar, when I removed it at the store's Ad Vise, the noise became gone.
Apparently, every time Bolt crossed a step, a part of Backrest's Bolt touched the Pillion Bar causing a strange sound.
It seems to be difficult for durability.
Whether it is an individual difference or not is unknown.