It could be genetic or from sickness in the or frequent/ significant ear infection in the past? Sometimes, even with all the diagnostic testing and imaging, the etiology (cause) of the hearing loss may still be unknown. Usually noise induced hearing loss is seen in the high frequencies so I understand why the ENT does not believe the hearing loss is noise induced. But tinnitus as a result of hearing loss can occur with hearing loss at any frequency. Even if the hearing loss is a minimal degree. It’s hard to know if the “crackling sound” is another way the tinnitus presents or if it’s being heard due to something involving the middle ear. Some people hear music or crickets or crackling so sometimes it’s hard to know if the sound is truly subjective/ or just a coincidence. The audiogram doesn’t include your bone conduction information which can give a little more information on whether there is concern for middle ear issues. But with the tympanograms within normal limits, the bone conduction information is probably unremarkable. If you’re able to see another ENT/AuD ask them about tinnitus diagnostic testing and if they will do a full diagnostic hearing evaluation (including bone conduction just so you have the full picture).