or even mild tension over your ears/near your temples?
The muscles that run from your neck up over the mandibular joint can cause tinnitus and muffled hearing. Push a finger behind your lower joint, just below the hollow under your ear. If that's sore, then what you have could be simple muscle tension.
I have temperomandibular disorder as a part of my fibromyalgia, and it gives me ringing and muffled hearing when those muscles are tight.