940 GLE 1992 60K miles mint shape

I've recently noticed a slight grinding sound (not squeeling loudly but crunching quietly) that quietly comes from the front brakes, not sure if both sides or not... The pads and rotors were replaced 2 years / 15K miles ago. I have been periodically looking at the thickness of the pads and have found that they miraculously seem to be lasting forever.

Last night I decided to remove the passenger side wheel and take a peek. The pads (both of them) seem to still be at least 75% thick. The rotors do not appear to have any major wear or surface dents on them.

The grinding sound is on/off depending on the day. Up here in Montreal Canada, we have snow and salt, so I was thinking that maybe dirt/salt is causing this... but I have never really experienced that before. The calipers do not feel sticky at all.

Any suggestions? Of course, replacing the rotors and pads will solve this issue, but why if they look smooth and thick?

Note the brake pedal does not really vibrate significantly at all. Braking seems strong and even on both sides (as tested in snow with ABS). The grinding, or crunching sound is often heard/felt just before the car reaches the stop, not at high speed.

What do I do?

Thanks,
Greg Mustang

'92 940 GLE 16V B234F 60K miles
'89 240 DL B230 130K miles (just entered Volvo High Mileage Club)