Precise audio/video rendering

Dear JB,

For my project "Les super-héros de l'immobilier", I need to insert beeps.
This is a very tedious work.

Here is how I process:
:arrow: Cut the video twice at beginning and end of beep.
:arrow: Mure where it need to beep.
:arrow: Insert a fake beep sound.

The problem is that, when playing the resulting video, the beep is not always at the same time, depending on the timeline resolution chosen in Kdenlive.
Therefore, it seems to me that the audio editing is not very precise.
For my personal knowledge, could you explain why?

Can the quality of display (low, medium, high) help for audio precision?

I have to agree that precision is better than one month ago. But still, it is not perfect.
Can you explain why? When there are 25 or 30 frames per second, time resolution should be 1/25 or 1/30 of a second.

So a beep should be at the very same place.
Do you understand what I mean?

By the way, what is "Use drop frames timecode" in preferences.

Kind regards,