The sheer magnitude of their size makes me feel uneasy.

From Wikipedia:

Blue whale calls last between ten and thirty seconds. Blue whales off the coast of Sri Lanka have been repeatedly recorded making "songs" of four notes, lasting about two minutes >each, reminiscent of the well-known humpback whale songs. As this phenomenon has not been seen in any other populations, researchers believe it may be unique to the B. m. >brevicauda (pygmy) subspecies.

The purpose of vocalization is unknown. Richardson et al. (1995) discuss six possible reasons:[73]

Maintenance of inter-individual distance
Species and individual recognition
Contextual information transmission (for example feeding, alarm, courtship)
Maintenance of social organization (for example contact calls between females and males)
Location of topographic features
Location of prey resources

It's fascinating how little we understand blue whales. They're the largest animals on the planet, out there singing songs, and we have no idea why.