picture of bellbox, video may help confirm as very quiet means absolutely nothing unfortunately.
Is it quieter than normal? or does it just sound quiet.
It could be right for that bell box or its setting.
For example:-
bell boxs are rated for the sound level in dB at 1M these vary.
Some have different settings also, SAB, SCB and low power mode, the quietist would be SCB as it draws least current, the next is low power and then SAB.
Some models have 1 piezo and others have 2. 2 piezos being loudest and that uses more power.
Faulty piezo may sound quiet or abnormal.