For mine, it seems to just be her curiosity/happy sound. My first hedgie Macy and then my current one Libby both made/make the sound. It's always when they are exploring, sniffing, and looking around. When she's on me and starts sniffing she'll make it and when she's in her cage walking around she'll make it. They only "angry" sound she'll make is her huffs when I bother her when she's sleeping.
With Prickly love, Libby Lou and Chelsea Kay!