It sounds like distant cannon fire, but a quick glance towards the Indian Ocean confirms the noise is coming from the gigantic creatures who give these waters their nickname: the Humpback Highway.
Two whales start breaching barely 200m offshore, the mighty whacks of their tails and pectoral fins on the water producing a sonic boom like the echo of guns.
Fifteen metre creatures weighing some 36,000kg can generate one almighty rumble.
Their acrobatics provide us with 20 minutes of inspiring natural entertainment.
"Wow! I haven't seen anything like this in years," enthuses Sean Blocksidge, whose company guides visitors around WA's Margaret River region.
"I've seen 20 in a day before, but not as close to shore as this.
"About 30,000 humpbacks, blue whales and southern rights are migrating down the coast to Antarctica and back. That's 60,000 chances a year to see them.
"It's a whale highway out there."
Migration season from June to December provides an extra treat on one of the world's great nature walks.
The Cape To Cape trek, from Cape Naturaliste lighthouse in the north to Cape Leeuwin in the south, is one of Lonely Planet's top 10 walks in the world.
It covers 130 kms of stunning coastline, but it's easy to dip in and enjoy stretches of just a kilometre or two.
The sea breeze is fresh and bracing.
"It's got to be the cleanest breeze in the world," says Blocksidge.
"Antarctica is that way (south), Africa is that way (west), and it's coming from right between them."
Other rewards include spectacles like the rugged Wilyabrup cliffs.
"Ninety-eight per cent of locals have never seen these cliffs," said Blocksidge.
He also reckons 80 per cent have never been up the river that gives the region its name.
We set that to rights first thing in the morning with a gentle canoe trip up the Margaret River.
The wind is a zephyr, the water is calm and the paddling is easy.
It's a tranquil start to a day that will also bring us close to the rare Baudin's black cockatoo, a threatened species endemic to this region.
Two of the birds perch on a tree 10 metres away from us on the track, and soon we are surrounded by a flock of a dozen.
"They are scarcer than polar bears," says our guide.
"Some force out there is giving us a very lucky day."
There's only one way to cap it off - with a glass of the chardonnay that has made the area one of Australia's premium wine capitals.
An Indian Ocean location is important - somewhere like Bunkers Beach cafe, or just about anywhere along the Cape To Cape track.
As the sun dips down, you might even see another whale.
IF YOU GO
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The writer travelled independently to WA, where he was a guest of WA Tourism.