LM386 no output with input signal below 2V
With the addition of "R17" (C17) before the digital pot, the voltages present on pin 5 of the pot, for any typical input signal, will settle to an average of zero volts since capacitors block DC. So the AC signal being fed into the pot, if it were 0-3.3v from a microcontroller, is now -1.65 to +1.65v, which 

To quote the MCP4131 Datasheet, 


  The terminal A pin does not have a polarity relative to
  the terminal W or B pins. The terminal A pin can
  support both positive and negative current. The voltage
  on terminal A must be between Vss and Vdd.


So you are placing as low as -1.65v on a wiper pin with these maximums as defined in the datasheet:


  Voltage on all other pins (PxA, PxW, PxB, and
  SDO) with respect to VSS .................. -0.3V to Vdd + 0.3V


Try it without C17 and it will likely work. If it still misbehaves, then keep C17, but bias pin 5 (add a resistor divider to it from +3V3 to Vss) to around +1.65v or slightly over. Doing so should prevent the signal from going negative into the pot.