Induction surface started making a barely noticeable high-pitch whining noise, even when it is not in use, is this dangerous?
Glad you are getting this checked out.

As Steve mentioned, it sounds like the power supply or the supporting electronics for the hob is starting to fail. To be on the safe side, I would isolate the power to it if at all possible (UK hobs are required to have a wall mounted isolation switch).

Certified electrical appliances are designed to "Fail safe” so the risk of fires etc. is small, but your hob is sending you a clear warning sign that it is not very well and should be turned off. Depending on the nature of the fault, this may eventually result in absolutely nothing at all (apart from mild irritation), a totally dead hob, a small bang, or indeed a big bang. The greatest risk you are probably taking is that your insurance company will not cover you should something adverse happen and they prove you continued using the device despite being aware of it malfunctioning.