Better Vampires and Immersive Sounds Compendium both change the sound effect for the vampiric drain spell to make it quieter and less annoying, but B.V. just makes it sound like the detect life spell, while I.S.C. has an actual unique sound effect for it.  B.V. Makes balance adjustments to the spell as well as sound adjustments, sadly they're both in the same entry meaning one mod will entirely overwrite the other mod's changes completely, that's why a compatibility patch is necessary.

This .esp is simply combining all (2) conflicting entries from B.V. and I.S.C and combining both their changes (except without including B.V.'s sound changes) making the mods work together properly.

You can easily do this yourself in Tes5edit by finding the conflicting entry and just copying everything under "sound" from ISC's plugin over to BV's plugin for the 2 conflicting entries there are. All I did was put the final product in an .esp to make it easy to turn on/off.

There's also another .esp under the misc files which simply undoes better vampire's changes to the sound (making it vanilla), it is incompatible with immersive sounds compendium though.