the sound problem is quite familiar and I thought so is the way to fix it.
if you are using sounds from Kunos, you can "easily" fix it yourself
I'm planning to post a new update, but I'm waiting for Kunos to release new update, so that I don't have to re-release fix in case it gets broken again
to fix sounds for ALL MODDED cars, using ANY KUNOS car sounds do this
> locate latest GUID.TXT , you should find one somewhere in system/sounds ( sorry, don't have AC here, can't tell you exactly )
> copy GUID.TXT into the car sounds folder and replace the one that's there already
> copy sound.bank file of your chosen car into the modded car and rename the file so that it matches the kn5 file name ( say BMW_E30_M3.bank to NISSAN_PRIMERA_BTCC.bank)
> edit the GUID.TXT file and replace all "source car" with "target car" ( search/replace "BMW_E30_M3" to "NISSAN_PRIMERA_BTCC") ( it will replace also things like _DTM, _GrA but that doesn't matter)
> DONE, lauch game and enjoy
this can fix any car and any sound
if it doesn't work you have done one of the following mistakes
- don't have latest GUID.txt ( or you haven't edited it and/or haven't replaced all entries )
- don't have latest sound.bank file
- your file names don't match your car name
let me know if you can't get it to work