Noisy WiFi Pod

I have one of the white hexagonal shaped WiFi pods. Over the last few months it has begun to get noisier and noisier. It sounds like an internal fan whirring. A short term fix can be switching it off overnight, however the noise returns after it has been back on for an hour or two. The noise is getting louder and does not sound like it is a good thing!

Any advice anyone can offer please?

Kind regards.