I was reading the question "Looking for an American 80's movie about a hazardous accident in an underground lab in the desert" when I was reminded of a combination SF/horror movie that had a very similar premise.
The basic plot was that the military accidentally (or intentionally) drop a missile or other explosive on an island. This explosive opened a gate /cave to a path deep below where another civilisation is based. These "species" looking like pale creatures/humans, with hell-blue eyes and wearing sort of a wig, in baroque style, (like mozart). They're living in a group, can't stand light and break most of the brighter lights. They couldn't stand high sounds (think it was a sonar, the team that was examining the cave and living below) used to scare them.
I remember that the high sound was the cause of the murdering of the examining crew and couple of military guys, because they couldn't stand the irritating frequency.