CLASSIFIED: Acoustic Surveillance Report

Audio monitoring systems have detected anomalous patterns in ventilation networks. Frequency analysis reveals structured signals that repeat on irregular intervals.

1. North Corridor (Ventilation Shaft 7B): Three distinct knocks followed by two-knock response pattern. Repeats every 47 minutes. Source location untraceable.
2. Archive Storage (Sublevel 2): Magnetic tape labeled "1977_11_dave" found in secure vault. Tape spool empty, but case contains micro-inscriptions reading "the vents remember."
3. Loading Bay (Service Entrance): White chalk markings appear on concrete floor despite daily cleaning. Pattern resembles architectural blueprints for non-existent facility wings.
4. Server Room (Climate Control): Dust accumulation on fan blades forms the sequence "D-A-V-3" before being disturbed by maintenance personnel.
5. Stairwell B (Emergency Access): Step 13 produces 440Hz tone (musical note A) when weight sensors register zero occupancy.

Signal analysis indicates intelligent origin. Pattern recognition algorithms classify these as "echo responses" rather than random environmental noise.

checksum: 77b9-walk-softly

anomalous signals • personnel file

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