Id rather have them hum then whistle

Humming is OK as long as the toilet holds a tune BUT if your really against the humming sound you can try to throttle the valve under the tank and it should slow the velocity of moving water.

If that doesn't work you may have to replace the flush valve

Thank you for your prompt response.

Unfortunately, the toilet is not playing my kind of music, so I most certainly will try your suggestions.

Best Regards

Feel free to keep me posted