I have a Now TV box I also have my phone line and broadband through them as well so was not purchased separately, I seem to have had a problem the last few days. The box has been reluctant to be recognised by my TV and then started overheating, I followed all the overheating advice, I also replaced the HDMI cable for a better one. However today it has started making an awful noise like a fan noise and can be heard over the television and the dog. I have turned it off but wondering if anyone else had a similar issue? Also the box had only been on 5 minutes.
Have you tried doing a factory reset?
Otherwise sounds like it is on the way out. For your reference NOW no longer make or sell their own devices so you will need to buy a new device making sure it’s supported from this link. Unless your TV is supported.