You can use the War3 Model Editor:
1. Load your file.
2. Go to "Windows >> Sequence Manager".
3. Locate the Death Animation and double click on it.
4. Find the "Interval >> From" box and memorize the number in that box.
2. Go to "Advanced >> Node Manager".
3. Right click on a blank spot and select Create Event Object.
4. Don't rename it for the moment.
5. Right click in the Event Tracks box, select Create New and type in the number you have memorized.
6. In the "Event Data >> Type" box select SND(Sound).
7. In the "Event Data >> Data" box select the desired sound, for example DFOO - FootmanDeath.
8. In the "Identifier" box type in [x] and leave the "Misc >> Global Sequence ID" to (None).
9. Now Memorize the 4 letters under the "Event Data >> Data" box.
10. Click Ok
11. Rename your UNNAMED Event Object to [SNDX****] where you replace the [****] by the 4 letter you've memorized,
it should look like SNDXDFOO if you've chosen the Footman's death sound.
Hope this helps, cheers