White and Pink Noise Generator Circuit - Cryptic AC Analysis
If we simplify the source to be R2+R3 and neglect the effect of R8 for an intuitive analysis, we see the impedance ratio as the maximum voltage gain if the transistor was an Op Amp with infinite gain. 

Let's assume a frequency well above all the RC breakpoints to neglect the cap impedance.  This is a negative feedback (NFB) transistor amplifier where the open loop AC gain is reduced by the ratio of the Rf/Rin.  

As you have computed , Rf=14.5k but Rin=R2+R3=44.6k
Thus Av = -0.325 = -14.5k/44.6k  or ~ 0.3

The ratio with 1M /44.6k= 22.4 but is reduced to 8.4 by the open loop gain of around 200 and collector R=5k6 of current feedback to the base.

Symbolically below.  The gain values were verified by simulation for the cases of 390k open and closed below.







simulate this circuit &ndash; Schematic created using CircuitLab

Graphically as follows using BODE asymptotes and the intersection being the breakpoints using an RLC Impedance Nomograph shows that the frequency response is almost half order where 1st order is 6dB/octave or 20dB/decade or a slope of 1 order of magnitude of impedance per decade of frequency.