Your concern is that you get the measurements within the 100-110 mm sag range , if you can't achieve the sag numbers at the recommended spring length then , yes, the spring is incorrect rate for your weight
So when you are manually moving the suspension up/down , even now after checking/adjusting , (i am assuming by grabbing the rear wheel) , you can't see/feel anything moving on its own in the initial stages of movement , that would indicate a bearing or something else worn in the swingarm , shock , wheel bearings , linkage , anything ??
The noise has to be from something with slop , weather it be a bearing , bushing , or spring (are you positive the spring currently on the shock is for the Showa ?? , a KYB spring might still fit but fit poorly enough to make noise/bind , sometimes (especially from eBay sellers) they don't specify if its a KYB or Showa spring when reading the add , so you have to pay close attention .... not saying this is the case , but it is possible , as i believe KYB springs are larger in diameter slightly
Weiser , Idaho