If I hadn't known, I might have hazarded a guess that it was the noise of an experimental orchestra tuning up in a cowshed, in the rain. Or perhaps someone revving a reluctant lawnmower engine at the same time as oiling a squeaky door and playing a rusty penny whistle in a cow shed, in the rain. In fact it's something much stranger than almost anything I could imagine happening in a cowshed in the rain. It's a mating song millions of years old, constantly evolving, mind-shatteringly complex and not uncoincidentally beloved of the New Age movement.

Whatever happened to whale music? There was a time when it was the must-have soundtrack for flotation-tank junkies, deep tissue massage and any other relaxation method you care to think of, and wasn't it the thing that everyone wanted to listen to when they were giving birth? Today, however, it has become shorthand for unsophisticated, hippy-dippy New-Agers. Apparently it isn't even considered much use for calming the mind any more. "We deliberately try to avoid that kind of soundtrack," says Sharon Scott, marketing manager at Champneys health resorts. "We choose music that is soothing, like water or bird noises. If we have anything as specific as whale music ... well, we tend to get a lot of complaints. Whales put people off." Massage therapist Anouchka Sterling agrees. "I don't use it. I'm not sure if the high pitch of their cries is conducive to therapeutic massage."

But whales dreaming of their chance to make it big in spa soundtracks need not despair. "Personally, I don't really understand what's relaxing about whale music," says Ian Samuels, sales director of the lifestyle CD company Global Journey. "I'd rather listen to a good thunderstorm recording. But whale music is making a bit of a comeback. It really had died a death a few years ago, but in the past 12 months wildlife and nature sounds, including whales, have become very, very in again. They're among our best sellers now. When it comes to what's trendy in relaxation, it's swings and roundabouts, like with everything else."

Whale music was, perhaps, a victim of its own early success. Most of what we think of as generically "whale" is in fact the mating song of the male humpback. In the 1960s, the biologist Dr Roger Payne and his colleague Scott McVay discovered that the sounds made by humpbacks were actually rhythmic, repeated patterns - and therefore songs. (He also theorised that the lowest, loudest sounds they make can travel across oceans, a theory proved true two decades later as Dr Chris Clark, on the east coast of America, listened to the sounds of whales migrating out of the Norwegian Sea into the Atlantic.) Payne's LP, Songs of the Humpback Whale, was released soon after and is still the bestselling natural history recording ever. A copy of these recordings was also given away to the ten and half million subscribers to the National Geographic Magazine, necessitating the largest ever single print order in the history of the recording industry. All in all, that's a lot of whale music floating around. It is perhaps no surprise that people had eventually had enough.

But now, according to the sales figures, whale music is back. "People are really stressed out at the moment," reasons Helen Faulkner, founder of Ocean Heart, a company that promotes interaction with whales and dolphins, "and whale sounds in particular seem to really affect people. It gives you a great sense of stillness and peace. It's very comforting." The exponential spread of alternative therapies and healing may also have given the whales a boost. The bestselling whale music CD on Amazon is currently Reiki Whale Song by Kamal, specifically designed for use during treatments. Dr Robert Jefford, chair of the UK Reiki Federation, says: "Music isn't essential for reiki, but most patients do opt for it. It certainly seems to help the session go better, because it helps people to relax. Whales are beautiful creatures and they make wonderful noises. Though it's mainly women who like it, in my experience."

There is anecdotal evidence of whale music stopping babies crying, that the sound has soothed foetuses, women during childbirth and people who are dying. Though no one seems entirely sure why. Samuels says: "The whale's moan is long, slow, contains a range of pitches, and is repeated in patterns. These characteristics make it perfect for relaxation. And people associate it with the tranquillity of the ocean." The humpback whale's song has a distinct structure and a singing whale will typically repeat his song - itself made up of repeated phrases - over hours, or even days. Samuels suggests that people listening to whale music find that their breathing unconsciously slows to match the whale notes. Faulkner adds: "Whale music is a very deep, resonant sound. It feels like it enters your body and vibrates."

Whales are mysterious and fascinating creatures, but surely this is mainly because they live a long way away in the middle of huge oceans and we don't see them that often? Perhaps if there were some in the garden, their song would lose its mystical resonance. Tim Wheater, a composer and sound healer who has released a collection of compositions set to whale song, says, "It is true that people have a rather woolly and benevolent view of whales, but having interacted with them in the wild I can say that they are just the most amazing creatures. They're very inspiring, and so huge and ancient. They make you feel mortal, more human. They are quite frankly hugely superior and hugely intelligent. The song is the male singing to his mate, serenading her with this glorious system of sound. It is conscious and innate and people connect with that."

And so, with great anticipation, I load my new whale music CD into the player. At first I am simply annoyed by the ever present watery rushing sound. And while they may woo the humpback females, the sounds - a mixture of lowing, squeaking, whines and whistles - are not in themselves delightful or charming to my human ear. But then, to my surprise, my cynicism circuit becomes briefly waterlogged and I find myself feeling - yes! - moved to listen to such private singing from the oceans' dappled and indigo depths. I'm not saying it's going on my iPod or anything; just that, as Wheater says, "It is the adaptation of the great song, the one song of the universe." And that, you will have to agree, is quite a song.

· Listen to a selection of whale music and watch Paul Burgess's powerful film about the battle to save the Thames whale at theguardian.com/thameswhale.

· The remains of the Thames whale go on display at the Guardian Newsroom, from Jan 22-27. For a free ticket, ring 020-7239 9993 between 10am and 6pm.

Listen to whale sounds, clip 1

Listen to whale sounds, clip 2

Listen to whale sounds, clip 3