Pseudoarthrosis or hardware failure: The patient has recently undergone a fusion at C4/5/6, and the presence of pain and a crunching sound at the site of the fusion, as well as above it, suggests a possible complication with the fusion, such as pseudoarthrosis (failure of the bones to fuse) or hardware failure (loosening or breakage of the surgical implants).

Adjacent segment disease: The patient's symptoms above the level of the fusion (C1 or C2) could be indicative of adjacent segment disease, where the levels adjacent to the fusion site begin to degenerate and cause pain.
Herniated disc: A herniated disc at C1 or C2 could cause pain and crunching sounds in the neck, as well as radiate pain to the ear.
Osteophyte formation: The formation of bone spurs (osteophytes) at the levels above the fusion could cause pain and a crunching sound as they rub against other bones or soft tissues.

Vertebral artery dissection or injury: Any trauma or injury to the neck, including surgical complications, can cause a vertebral artery dissection or injury, which can lead to stroke or death if not promptly diagnosed and treated.
Spinal epidural hematoma: Bleeding into the spinal epidural space can cause compression of the spinal cord and lead to serious neurological deficits or death if not promptly diagnosed and treated.
Infection (osteomyelitis or discitis): Infection of the bone or disc can cause pain, swelling, and neurological deficits, and can be life-threatening if not promptly diagnosed and treated.

Craniocervical junction instability: Instability at the junction between the skull and the cervical spine can cause pain, crunching sounds, and neurological deficits.
Eagle syndrome: An elongated styloid process or calcified stylohyoid ligament can cause pain in the neck and ear, as well as a crunching sound.
C2 nerve root compression or injury: Compression or injury to the C2 nerve root can cause pain, numbness, and weakness in the neck and arm, as well as a crunching sound.