To Alex:

First of all your SOUND.TXT is based on oudated version... current version have more sounds, also some indexes are changed.
So the question is why you are using outdated files?
You need to move your changes to latest version with latest Patch 3 (look at the bottom of this post).
Or at least tell us version you are using - like - my work is based on SE v.#.#.#.# with Patch # v.#.#.#.# installed.

Anyway...

Bug found in this version:
ENGINE101.WAV too long file name (typo? - must be 8.3 characters max when here we have 9.3) should be renamed to ENGINE11.WAV
ENGINEDS.WAV alternative sound set to non existing sound index 530 (probably was intended to be 5300, which is used as alternative in all other custom engine sounds here)
I'm not sure if this is wrong, but one of new Song ID is set to big number: 19580 (I have leaved this as is).

Also all listed files must be in SOUND folder:

(list of custom sounds)
ENGINE6.WAV
ENGINE7.WAV
ENGINE8.WAV
ENGINE9.WAV
ENGINE10.WAV
ENGINE101.WAV   // Need to be renamed to ENGINE11.WAV
ENGINE12.WAV
ENGINE13.WAV
ENGINE14.WAV
ENGINE17.WAV
ENGINE18.WAV
ENGINEPX.WAV
ENGINERK.WAV
ENGINEPV.WAV
ENGINEDS.WAV
ENGINEST.WAV

Wrong wav file format may also cause problems. Have you done the sounds following such procedure:
http://www.cwaboard.co.uk/viewtopic.php?p=104889#p104889
?
(plese note that some custom made sound are done bad and need to be converted, so check if the files are in correct format even if you hear the sound in game)

Of course all new sounds need to be linked in other text (script) files to work.

If you are care about zombie and robot modes you need to update corresponding files either.
Look FILE_GUIDE.TXT which is included with Patch 3
(Warning: don't use patches on your customized version - it may wipe out your customization - you need to apply it to clean copy of SE, then copy your customizations there).

I have updated and fixed your SOUND.TXT - all custom sounds moved below originals and older version which is keeped to keep compatibility with older files that you are probably using.

QTZ.
