Bluetooth speaker

Hi there,

Here is a Bluetooth speaker I've made some time ago. It consists of 1 x 18650 li-ion battery (usually lasts for 2 evenings filled with music at moderate volume), Bluetooth audio module, a USB charger module and a tiny PAM8403 audio amplifier with a potentiometer. The speakers are the most expensive parts of this project - I've chosen BF37 due to their good bass response (for their size) and generally high sound quality. The housing volume is around 0.9 L which follows the simulation by WinISD. The membranes of the speakers are protected by a 40mm fan metal covers (a little bit bent to match the speaker screw hole spacing). My intention was tu use the PCV pipe, but to be honest - I was too lazy to cut pipes and drill holes, so I decided to 3D_print the enclosure entirely.

After assembling all together I realized that the unwanted noise is clearly hearable at absence of the sound - the reason was a ground loop problem. To get rid of it I had to apply an electrical modifi