Terrified...

I turned my bed side lamp off at roughly 23.00 and put my head on my pillow. Just as I was about to slumber I hear a noise in the house. It was one of those noises which completely freaks you out. It's not that it was super loud or anything, but it sounded suspicious. One of those noises that you don't normally hear.
At this moment I froze in my curled up position in bed, swaddled by my duvet, and I could hear my heartbeat pounding in my ears. I lay still for a while, hardly breathing. Listening for that sound again. I heard it several times and started to freak out even more, as I was almost certain someone was in the house.
In these situations, I usually am too afraid to even breath, and will absolutely not move form my frozen position, not even to turn on the light and sit up in bed. But after a serious debate in my head of the consequences of me not getting up and investigating, I finally rolled over and turned on the light. I then sat up and reached over for my phone on my bedside table. I quickly punched in 112 into my phone (just in case), but didn't call. I then put my feet on the ground as quietly as I could and snuck over to my door and put my ear against the door. At this point I felt my adrenaline rushing though my body and my  heartbeat was pounding like never before. I then heard the sound again and mustered up enough courage to open the door. Just in that instant I recognized the sound I had heard as the sound of water dropping from a tap. I cautiously headed over to the bathroom but it wasn't coming from there, so I stood still for a while, listening for the quiet "plop" sound again.
It wasn't coming from downstairs, so I headed into the living room, thinking it was coming from in there (weird.. I know). But apart from the buzzing lights we have in there it was silent. So I headed back to my room, when I heard the "plop" once more. It then occurred to me that it was coming from my brother's radiator in his room. As his room is right opposite of mine, and his door is open as he isn't home, I could hear it very clearly from my position in bed. I cannot describe the relief I felt when I finally figured out where the strange noise was coming from, and what was causing it. I let out a huge sigh of relief and instantly felt a bit queasy, but headed back to bed to try and calm myself down by listening to calming music and watching 2 clips of Robin Williams' stand up on YouTube. Now, after writing this, I am going to catch some z's.