1. NEVER lubricate brakes with anything that reduces friction
2. Check the brake pedal and brake linkage, is the sound coming from INSIDE, or outside?
I had a squeak coming from my brake pedal linkage, up under the dash, I coulda swore it was coming from outside the truck, but it wasn't.
Have a friend accompany you to a parking lot, and have them check if the noise is coming from outside, and if so, where, then find the cause.
its possible you have a slightly sticky caliper thats not realeasing pressure fast enough.