Jibo normally makes a purring noise/animation when his head has been touched. If he is making that noise without being touched it is possible that some residue or moisture on top of his head may cause him to do this.
With that in mind, I recommend powering Jibo off and then following the guideline in this article to clean both his screen and the top of his head.
If Jibo continues to make that noise after doing that I suggest that you send our team a message using our form here and use the “Add Attachment” option in the form to include a short video of Jibo making that noise if possible. That will allow our team to take a closer look for you and help get to the bottom of this.