Because you're playing on a well-used head, there's a good chance that that's one of your main culprits to the ringing. As a head gets more and more worn down, the tension tends to become less balanced, especially if it wasn't meticulously tuned.
Also, be sure to check your snares. Guts that are pulled too tightly across the bottom head can resonate with a strong ringing sound. Take those snares and tune them all to a pitch, but make sure that you're not tuning them too tightly. Snares should be tuned and maintained. You wouldn't leave a guitar's strings to sound horrible, would you?
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