Good idea as suggested above to check if any of the wheels are getting abnormally hot after a drive. Common causes for a squeak that goes away by applying brakes
- worn pads
- worn wheel bearing
- anti-brake-noise shims not working/missing/etc
- caliper not sliding freely along the slides
- warped rotor (any pulsation felt when applying brakes?)
- pebble or something is stuck in the wheel
If the brakes aren’t getting hot and there’s no pulsation, if that were my car’s problem and I’d check the front pad wear the easy way, by visual inspection done by just removing the wheel and looking, then I’d just keep track of it, monitor the problem, make sure it isn’t getting worse. If it starts to gets worse, I’d check the wheel bearings for play, the rotors for run-out, and take the front brakes apart to find what’s causing it.