Solved... I added,

gpio_pullup_en(GPIO_NUM_15);
gpio_pullup_en(GPIO_NUM_2);
gpio_pullup_en(GPIO_NUM_4);
gpio_pullup_en(GPIO_NUM_12);
gpio_pullup_en(GPIO_NUM_13);

After the the gpio_set_pull_mode's in a2dp_source/main/main.c and it works like a champ now on both of my boards.

I have two ESP32 WROOM 32s. One is a NodeMCU board, and one is a bare chip soldered onto a breakout. Both are using 4 bit SDIO to read PCM data from an SD card and push it via A2DP to a speaker. The NodeMCU board works more or less correctly. My bare board produces the following log.. and the speake...

I got A2DP source working with raw 44.1kHz PCM data streaming to a fidget spinner

https://www.youtube.com/watch?v=qr1t3I-Gxk0