Damage send/receive sounds (hitsounds and damage sounds) both use damage receive sounds.

[gordbomb42]

The hitsounds (sounds played when the player deals weapon damage to an enemy) and the damage receive sounds (sounds played when the player takes damage from an enemy) both use the same sound files, those being sounds/hit_indicators/damage_receive_default*. Hitsounds should instead use the sounds/hit_indicators/damage_send_default* sound files. This is especially noticeable if a mod is used to replace the default hit/damage sounds.