Squeal from brake

When I take my foot off the brake, there is a squeal or whistle. It’s sporadic and sometimes loud and long, other time low and short. It doesn’t seem to happen when the mechanic is driving. And they can’t determine cause.

JLC, More Information Is Requested.
Let’s Start The Conversation Rolling.

Your description of the symptom is very good.

However, it will save lots of suggestions and guesses if you could elaborate a bit on what has been done to diagnose the problem besides the roadtest by a mechanic.

Have all 4 wheels been removed for a thorough inspection of brake parts, for instance ?

Can you tell if the noise is coming from the dash board area, a wheel, right or left, front or rear ?