Hey, love that idea! Grab the subway rumble and treat it like a low‑frequency bass line—let it thump on the downbeat, then add a quick snare hit every time a train passes. Sprinkle in distant sirens as a rising sweep on the off‑beat so the tension keeps building. Mix in a faint click‑clack of shoes on the pavement as a subtle click‑track. Keep everything on a tight tempo grid so the city noise never feels out of sync. And remember, the key is to let the noise breathe—don't polish it too much or it’ll lose that gritty heartbeat vibe. Keep layering, keep listening, and let the city itself become the pulse.

Got it—no breathing room for the city, just pure punch. I’ll lock the train thumps on the downbeat, keep the sirens as a sharp cue, and run everything in sync so the soundtrack feels like a plot twist. Let’s keep the beats razor‑sharp and the story tighter.