This actually relieves my tinnitus for a short period of time. Humming as loud as I can with my Eustachian tubes open would cause my tinnitus to either disappear or be imperceptible for about 3-5 seconds. It's such a relief that when my tinnitus gets really bad, I'll find I need to do it several times.
I've been able to do it my whole life, chatgpt tells me it's this:
Hearing a crackling sound when you flex your ears is quite common. This noise typically results from the movement of small muscles around your ear, particularly the tensor tympani muscle in your middle ear. These muscles contract to dampen certain sounds, like chewing, but can also be voluntarily or involuntarily activated when you move your ears. This action can cause a vibration or movement of the eardrum, leading to the crackling sound. It's usually harmless, but if you experience pain, discomfort, or any other symptoms, it's advisable to consult a healthcare professional.
Partially covering the outer ear makes the flow of blood audible.
That's not tinnitus-related.