Arcade (lr-mame20xx) Audio crackling on custom refresh rates (CRT)

[jedcooper]

Hi there CRT freaks!

I'm using a RPi 3B+, RetroPie Buster, 17" pretty standard CRT, lr-mame2003-plus
(also happens in very same matters in lr-mame2010, lr-mame2003)
Other Arcade emulators not tested yet. I'd prefer the lr-mame2003-plus.

I'm creating my very own CRTPi interpretation for VGA 31 kHz+ Hfreq monitors. So far it's working great as I'm using it for consoles, computers and Neo Geo, yet. See my project and scripts here: https://github.com/jedcooper/crtpi-cooper

Now as it comes to Arcade emulation, staying at the default refresh rate(s) of 60 Hz or rather 59.94 Hz it's all fine too.

BUT creating custom refresh rates f.e. for
Mortal Kombat = 53.204948 Hz (hdmi_timings 1920 0 64 192 256 288 1 1 18 15 0 0 0 106 0 79450000 1)
the audio is crackling as if it were not right in sync.

I tried the core options Bypass Audio Skew on/off, Settings Audio max Skew 0,05 (default) -> 0,00, 0,10, 0,50 etc. Audio synchronization off etc. No change.
Only if I turn VSync off, audio is fine, but ofc then the scrolling gets off (jerky), because of internally running at 59,94 Hz I guess.
It's not synced to exactly 60,00 Hz, because if I use a 60 Hz modeline audio is also stuttering. So my guess is internally "hardcoded" 59,94 Hz.

Any experienced CRT refreshrate dudes(ses) here who might help me with this issue? :(

Where do I have to set Audio sync to my custom refresh rate, and NOT staying "globally" at 60/59,94 Hz?