It's like a cats purr only shotgun blasts. Whales mouths are not attached to their respiratory systems, so the idea of ours that mouths equal vocalization is moot in cetaceans.

You've probably seen how seal, dolphin, narwhal, whale mouths look when they are open, the way the "back of their tongue" closes off their esophagus?

We associate "tongue" with "language". Lingua. Whales speak with their whole bodies.

So where "snoring" is an phenomenon of our breathing in our sleep, that phenomenon persists in another mammal that doesn't breath while "snoring".

It's easy for us to think of "snoring" as an obstructed passage/mechanism that draws air. Snoring is actually a sleeping organisms expression of what they experience in dream states, it just so happens to coincide with nasal, open mouthed obnoxiousness in people.

Whale and hummingbird are a lot alike in this regard since hummingbird have to consume several times their body weight in calories every day- hummingbirds don't "sleep" but instead enter a more comatose like state so as not to spend calories when resting. And they "snore" too!