This usually happens because kdenlive is not smart enough to deal with multiple types of files, especially different frequency.
If you take a 44.1khz audio track and then add a 48khz track, you will definitely get the pops and clicks.
Use a tool like audacity or similar to do two things, flatten the audio tracks to mono and at least make sure both tracks have the same frequency.
I recommend changing both to 44.1khz.
After Idid this and reimported the trac........
ID3 2.4 can cause various MP3 players, especially on vehicles or even computers, not to play or at least not to display the ID3 tags.
In many cases though, since ID3 2.4 is much different than version 2.3, it will cause some players, especially in cars like Lexus not to play. Even on the computer, you may notice if you check the properties of the MP3 that it won't open or show any details (eg. frequency, bitrate and ID3 tags).
One symptom of this in a vehicle (eg. Leuxs,........