High pitch sound coming from Low-Dropout Linear Regulator (1117 3.3V) setup
It is possible that your LDO has become unstable and it is oscillating at a frequency that is audible and you hear it through the piezoelectric effect of the capacitors as Mike mentioned.

Keep in mind that the reason an 'Aluminum' or 'Tantalum' if often recommended for some LDOs Output Capacitor (such as TLV1117 or LM1117) is that these tend to have higher ESR (Equivalent Series Resistance) than Ceramic or MLCC Capacitors.

Although the AP1117 does mention it works with MLCC capacitors it still mentions it needs an ESR between 150 mΩ and 500 mΩ, while most Ceramic Capacitors today can have an ESR ranging from low as ~5 mΩ to around ~500 mΩ.

You have a few of options if you want to fix the issue:

1. You can use an LDO that doesn't require a minimum ESR, such as TLV1117LV: "Unlike traditional linear regulators that need a minimum ESR for stability, the TLV1117LV series are ensured to be stable with no ESR.".

2. You could try finding MLCC Capacitors with Higher ESR.

3. You could put a small resistor in series with C4 to ensure you meet with ESR requirements.

You can find more information on the topic of ESR and its importance on LDO stability here:


Selecting ESR for linear regulator stability
ESR, Stability, and the LDO Regulator
Linear Regulators: Theory of Operation and Compensation


EDIT- Adding the following resources:

You can find more about Capacitor's ESR Here:


ESR Control Multilayer Ceramic Capacitors
Analog Engineer's Pocket Reference, which you can Download (Pages 14 ~ 17).