I have a 1999 Subaru Legacy Outback Wagon. A couple days ago, I noticed the back RH (passenger side) wheel started squeaking/making a high pitch sound while I'm driving. It's gotten louder the last few days, and is most noticeable with the windows down and driving slow(ish, like below 60 mph). It stops while I brake, and occasionally will stop/start when I'm accelerating or coasting, but it mostly tends to make sound if I'm not braking. I just replaced the brake pads/rotors about 3-4 months ago, but that back wheel also tends to have that burning brake smell if I check it out right after a drive. From looking at other questions, it seems like it might be a result of the pistons getting stuck/not releasing fully after braking, wearing down the pads, and causing the little brake noise scraper thing to scrape on the rotor. The bolt that this back wheel's caliper slides back and forth on to open and close also isn't the OEM part (I bought the car relatively recently and it looks like the previous owner may have done a brake job himself and replaced the original bolt with a part that didn't quite fit exactly).
My questions are these: Does it sound like I'm diagnosing the problem (something wrong with the calipers causing the brake pads to wear too quickly) correctly? And if I am, is the best fix to replace the pads/rotors, or replace the whole caliper too?