Lubricate the sliding surfaces with moly or lubriplate and check for a sticking caliper. Sounds like you might have a worn pin or retention clip/mechanism. Examine all the parts carefully and replace anything worn, inspect the caliper boot for corrosion hiding underneath. Replace if necessary or rebuild the caliper. Doesn't sound like a major problem yet.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo