Asymmetric tinnitus — louder on one side, only on one side, or with a different pitch on each side — is more common than people realise, and usually it reflects asymmetric hearing loss. Your audiogram on the affected side likely has more high-frequency dip than the other, and the tinnitus follows that dip. Common reasons for asymmetric loss include unilateral noise exposure (the side of the head you turn to a band, the ear that takes the gunshot, the side that takes the phone in a noisy office), an old ear infection that scarred one eardrum, or just normal biological variation.
Most asymmetric tinnitus is benign and explained by the audiogram. But a small fraction is caused by something on the auditory nerve, most often an acoustic neuroma — a slow-growing, non-cancerous tumour. That is why audiology guidelines recommend an MRI scan in cases of clearly asymmetric tinnitus, especially when paired with asymmetric hearing loss, dizziness or one-sided fullness.
If your tinnitus is markedly worse on one side and you have not been worked up, ask your GP for a referral to ENT or audiology for an audiogram and a decision on imaging.