Question of the day

I was sitting in the bath last night enjoying the sound of rain on the iron roof of the house. Then something happened to disrupt my serenity. It was a dripping tap. It was horrible. Drip. Splat. At uneven intervals. And it just made me wonder, why is rain on a metal roof one of the best sounds ever, when a dripping tap is so annoying? Why doesn't falling rain sound like a million dripping taps?