2000 V70 SE, AW-5, 238K miles

This car drives up and down a steep and curvy two-lane three mile mountain grade almost every day, with just me in it as the driver. Last week, the car transported four full-sized adults plus a couple hundred pounds of luggage to the airport. When applying the brakes going down the hill, I felt and heard what I'd call a scraping, vibrating sensation. Not loud or harsh like metal on metal, but it was certainly there. Once the car lightened its load again, there has been no more noise or vibration this past week.

First thing I'll check is the front brake pads and rotors; however, when I had the tires rotated last month the shop didn't say anything about worn pads or rotors. They're pretty good about calling attention to any needed maintenance. Tires are on the last third of their tread life, with 35K miles and due for replacement in about 7K more. I expect at least the front brakes will need pads and rotors then too.

Any experience with symptoms like this?