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Isolate the leak area by reducing the sensitivity of the unit and by pushing the tip of the rubber focusing probe up to the test area, checking a small section at a time. In some extreme instances, when the leak check is difficult at 40 kHz, try to "tune in" to the leak sound by "tuning out" the problem sound. In this instance adjust the frequency until the background sound is minimized and then proceed to listen for the leak. 17 1. SHIELDING TECHNIQUES Since ultrasound is a high frequency, shor