No but the alternator should be fine: the voltage is always higher, when engine is running.
I got one of these as well, and use it to measure the voltage: it fluctuates between 14v and 15v actually, just once it reached 15v and the rest of the time it stay around 14.3v
A fellow Suzuki Celerio owner suggested, the interference might be high frequency interference. Which you can solve by placing a Ferrite ring, so I have ordered some of these as well.
These things you used to find very commonly on electronics: I remember having these Ferrite rings, on cables from game consoles. So I'm going place it closely to the RCA connector, near the headunit.
And the Car Camera Filter, that one has to be removed: it makes things even worse. But this going be a long project, because delivery from AliExpress tends to take up to month sometimes.