工业激光钻循环底噪

Seamless looping industrial laser drill ambience, one second that loops perfectly. A steady 90 Hz mechanical rumble, a light 3 kHz sizzle on top, and a faint rhythmic 4 Hz pulse from the drill motor. Controlled, even, moderate level, machine-like, not harsh, with clear headroom to spare. No reverb, no musical pitch, no melody, no fade at the loop point.