noise of SSM2019

Dear Sir/Madam,

We are using SSM2019 Self-Contained Audio Preamplifier.

We have observed the noise on our system. Pls refer to the attached file.

sheet1. Our test circuit diagram.
sheet2. Waveform which the noise occurred.
sheet3. Normal waveform.

It is irregularly-recurring noise and the repetition is not regular.
Quantity of the device that this phenomenon occurred :9pcs/460pcs

We would like to know the cause of this noise.

It would be greatly appreciated if advice could be gotten.

Sincerely yours,