My guinea is about 1 year and a bit s, for a long time now every time he cleans his bits or his back he makes almost like a moaning noise. If I was to touch a certain patch or his back he’d go for me. (His a loving guinea pig just has a thing about the patch) his done it for ages and his always biting that patch of hair. He has no mites or anything, he doesn’t scratch loads. I do have to clean his bits for him now and then as his lazy with it.