The Gog version has the soundfx with wrong pitch, it's easily hearable starting in the mansion and jumping, sounds strange.
I saw a tool for fix that called TRLE SFX Edit but there's no .sfx files in this version.
Readme says:

This tool is made to fix sounds from tr1/2. To use, open the sfx of your wad and select the sounds. Normaly the following values work correctly:

RAD 20
PIT 30
VOL 70
CH 0

There's any way to fix that in the Gog version?

I recommend that you first try the Windows version. If the issue has anything to do with the original game executable or DOSBox (both of which the Windows version bypasses), that should fix it. See the following thread:
https://www.gog.com/forum/tomb_raider_series/tomb_raider_1_native_windows_and_resolution_patch

If you really prefer the DOS version, there's a SETUP.EXE in the TOMBRAID sub-folder that's used for setting up the sound card for the game. Perhaps changing the sound card settings in there would help. You'll need to run DOSBox from the DOSBOX folder and then mount the game folder before you can run it, of course... oh, and make sure that the settings for IRQ and such that you set are also set in the .conf files.

As for that SFX Edit app, I've not heard of it and have doubts that it's necessary, but if you're determined to try it, the .SFX files that you're looking for are probably in the .PHD files (which are the "WADs" that the program mentions). Those .PHD files are inside GAME.GOG, however, so you'd need to use UniExtract (link in the thread above) to extract them, edit them, then put them back (IZArc may be able to do that)... or use the Windows version linked above and just put them into the DATA folder. Either way, that's a lot of work and it may not work.