Hello, have been reading here for a long time, but this time I was hoping to ask for some of your expertise. This is my first ever PCB design project, so please forgive me my mistakes

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You can read more about the purpose of the PCB and the project
on my blog.
So basically, I have developed a PCB to add bluetooth audio to my car by faking the CD changer. I did this with an ESP32 for bluetooth and an external DAC (PCM1789) for the audio outputs. I have two versions of the PCB which are shown below. The larger PCB is version 1, the smaller PCB is version 2.
Version 1In version 1 I used a LM2940 linear regulator to go from 12V to 5V, and a Recom R1SX-0505-R to create an isolated 5V for the analog part of the PCB. I used a separate ground plane under all the audio components. Audio/noise performance is maybe not perfect, but acceptable for me at least. The problem with this PCB is that while it was working perfectly on my desk, the linear regulator produces too much heat in the car (14V instead of 12V), between 1 and 2 watts which it can at least with my PCB not dissipate triggering overtemperature shutdowns on the LM2940.
Just the audio and power components of the PCB:

Top layer:

Bottom layer:
Version 2To solve this in the second version I changed the LM2940 to a LM2594 switching regulator to go from 12V to 5V. What I also did as an experiment in this design was remove the isolated DC/DC converter because I had included this as a precaution and I was curious if it was really needed or not. Again I used a separate ground plane under the audio components, this time with a small connection to the main ground. So this PCB also worked fine on my desk, but in the car the audio quality is not acceptable. There is an audible high pitched whine on the audio outputs which changes with the revs of the engine of the car

. To give an indication for the level, if you play music it is not too noticeable, but I listen a lot to audiobooks, and there you have more silences between sentences so there it is more noticeable. So, it is not extreme, but annoying enough to not want to live with it.
Just the audio and power components of the PCB:

Top layer:

Bottom layer:
Next stepsI am hoping with the next iteration to create the final PCB that solves both audio and temperature issues. Therefore I would like some input from you guys.
- Are there any obvious mistakes or poor design choices in my PCB which could lead to additional noise?
- The most obvious solution for me is to combine the two approaches, use the LM2594 switching regulator in combination with the Recom R1SX-0505-R. Do you think this will fix it 100%, or will the fact that the 12V to 5V is a switching regulator instead of a linear one still create more noise, regardless of the isolated DC/DC inbetween?
- The second choice could be to change the PCB design of design 1 with more thermal vias and copper to try to dissipate the heat, or change to a through hole package for the LM2940 which can also dissipate more. Still you are creating a lot of heat
- Are there completely different configurations or solutions for this design which are more commonly used that I overlooked?
I guess question 2 is the main one for me, since I lack the experience and insight to judge this

. Would the performance of this layout be the same as version 1? close to version 1, or rather closer to version 2?
Thanks in advance for thinking with me. I am hoping that my next design will be the final one, which is why I would like some additional input rather than just continuing with the trial and error process
