In my initial observations of the first laptop (IBM Thinkpad T60) the laptop provided a clean audio signal from 0hz and above up until a week ago that signal became noisy which was fixed by using a different laptop (Panasonic CF-29) that has grounding.

Noisy Signal with Thinkpad T60, ungrounded:

@ 1sec shutter

Clean signal with grounded Panasonic CF-29:

1.5sec shutter

Tests dB vs Hz

  1. Anomalous under 100hz:

2. Anomalous above 100hz:

To be continued….