It may be better to generate a diagnostics report and contact Sonos support direct. 

Best solution - contact support via chat - Support Chat

There Bot, but it will provide you to human.

p.s. Also you can perform Hard reset to unit and setup it from scratch - Reset Your Sonos

I would do a hard boot which is holding the lit area and at the same time plug the speaker in. I did that with a gen3 sub and it stopped making the popping sound if it’s similar. So sound comes out normally when listening to music or tv? Just curious. Good luck

Thank you for your answers. Just to clarify, the speaker does not react to hard reset or any presses. Also, connecting with the optical cable did not work. 
As soon as I turn on the power, there is a quiet pinging sound, and it seems to me that it is not coming from the speakers. 

Looks like hardware issue.
Best way - Contact support

Despite suggestions above, it’s better not to do a factory reset unless Sonos advises it. It’ll delete any info that might help identify the fault. 

Thank you all. The problem was solved by sending the speaker to a service center and getting a voucher. Tech support did not explain to me what the error was.