Myself and 2 friends were out of our car on Nevada Rt 375, 40 miles from Rachel, NV. Without warning, I/we heard the sound of a very low-flying jet go by us, low. (I am former Air Force, and am familiar with these sounds.) All three of us scanned the sky, my friends looking at higher elevations. I looked at low elevations and quickly did a 360º scan, knowing that if you have heard it, it's already gone by. None of us saw any craft at all. The continuing sound did not last long, indicating that it was probably very low-level. The day was clear and the visibility excellent. Did we encounter a cloaked jet fighter?