I just set up a new PiCar, with a Raspberry Pi 5. Everything seems to work so far, except that the sound from the speaker is very faint. I don’t have a heatsink installed and nothing looks damaged. I searched the forums for ideas including trying alsamixer, which says that the volume is already set to maximum.
Update for anyone else who encountered this; alsamixer did end up fixing it. I just needed to press F6 and change the sound card to snd_rpi_hifiberry_dac, and then I saw it was only set to 40%. I raised it to 100%, and now the sound is much better. (Before pressing F6, alsamixer was showing controls for Master volume, which was at 100% already.)