Sadhguru Explained Heart chakra | Anahata: The Unstruck Sound 

It's called tinnitus

​​@@cloakrabbit767tinnitus sounds 'external' like it's coming from somewhere outside. Anahat naad feels like it's there but it isn't. Tinnitus can be heard all the time and will annoy the shit outta you. Naad can only be heard when you're meditative to a certain degree, and sounds extremely pleasing.

​​Ive found this experience has riden the tinnitus. But tinnitus is external but not from something outside the body. The tinnitus is the brain making sounds trying to compensate for sensation that is no longer available. So ive found once the sensation in body is available agian. And airways and pathways are cleared. Tinnitus will slowly recede. ​

He has also talked about same thing but in different name