Hello, Peter, and Welcome! The “dull thud” could be a matter of the striker/hammer resting on the gong between strikes, effectively muffling its vibration. I haven’t had to adjust mine, but I believe it is fairly simple, something on the order of lightly bending either the gong spring or the hammer arm. However, I’d probably suggest registering and asking your question on the NAWCC forums (http://mb.nawcc.org/index.php) to get more expert advice.