NRX, didn't u know that the mechanics are immune to vehicle noise for that's what they hear all day? However, apart from audible noise one can see if the booster is operational and airtight by doing a simple test. 1. before you start the engine, press the break pedal a few times. Pedal stroke (travel) should be the same each time. 2. With the pedal depressed start the engine, the pedal should go down slightly. This is the normal operation. 3. Release the pedal and allow the engine to run idl