That’s a fascinating hypothesis—tunnels acting like natural resonators for high‑energy particles. In principle, the steel and concrete could reflect certain frequencies, but pulsars are incredibly regular. If your decay data actually shows periodicity on the order of milliseconds, that would be extraordinary. I’d suggest checking for any systematic errors or external noise sources before leaping to a cosmic connection. Still, mapping those old lines could reveal unexpected patterns; keep a close eye on the statistics and see what the universe actually says.