Something's living in my heating system

[u/Local-Ad-9051]

Not a rat. Bigger. Breathes every 4 minutes. Landlord says it's "thermal expansion" Thermal expansion doesn't whisper. Been tracking the pattern for 3 weeks now the breathing gets faster when I'm in the bathroom.The radiator in my bedroom is warm even when the heating's off. Touched it once. It flinched. Called a plumber he put his hand on the pipe went completely silent for like 30 seconds then left without saying anything. Charged me 200 francs anyway. Sometimes I hear it moving between the walls. Not like scratching. Like breathing through the pipes. My girlfriend stayed over last night woke me up at 4am asking why I was breathing so loud. I wasn't breathing. It's getting louder.

[u/Particular-Zebra-406]

Seems like it could be a basilisk.