If I'm not mistaken, int 13 is handled correctly if you boot from an image.

I outlined instructions for Captain Blood (which has a similar problem) at Captain Blood Doesn't Start .

Don't know if this warrants bumping such an old thread... but when the game is configured for "SB Digital", I get continuous squealing from the PC speaker whenever a music track is playing (messing with sound card, cpu or cycles settings doesn't seem to help).
This is easily worked around by muting SPKR in the mixer, but might be worth looking into.

Seems like it only does that when the music is digital. If you choose GS or FM music then the sfx on the Soundblaster causes no speaker noise. The game may be using the MiniMod library for playing MOD files, because other games from the same time period using that library have the identical issue: Arnie 2, Chopper Duel. Hal-9000 commented that it's a speaker emulation problem, so perhaps the timer rewrite (which is likely to include at least parts of the speaker emulation, if not a full rewrite) will fix it.

I've been running into a number of titles with this issue, my current list would be...
Ortotris (1992)
Uncover It! (1994)
...both Polish games. I know I have a few other titles in my collection it effects.