Brakes - what should they sound like?

This past weekend we did our last camping trip of the year. We drove from Vancouver to the Okanagan Lake over the Coquihalla Highway with a top elevation of just over 4000 ft. On the way back we had long stretches of downhill with a speed limit of 120km/h which is where I noticed that my brakes were sounding strange, kind of like a drum. I thought this could be because of the relatively high speed and long braking periods but I wanted to run this by others to see if anyone else has experienced this. Since our trip the brakes feel and sound normal again on our daily commute.



Has anyone else observed this? Is this normal?