Welcome to the site !!
Did this noise just start out of the blue ?? , or was it something that occurred after the installation or maintenance of the clutch ??? , since it is a slipper clutch it would work differently than a stock clutch , it could be possible that there is a slack adjustment and that it might be loose and need adjusting .... I personally do not know enough about the STM Slipper Clutch to say it is a "normal" sound or not ..... but as noted above , some more detail on the issue might help diagnose the noise ......
Was the clutch in the bike when you bought it ??
Did you buy the bike new , then install it or have a shop do the install ???
Did it make this noise since installed or bike purchase ??
Did the noise just suddenly start up without anyone touching the inside of the clutch ??
The more details you give , the easier it will be to try to figure out if this is a issue or not ...... it sounds to me like it is working normal then something releases , which I believe that is how a slipper clutch works , is by slightly dragging , then engaging or releasing .....