There are times when I step on the clutch you can hear a very very soft spring-sounding "twing", not always though, maybe 3 out 10 times, once in a while... should I worry about this or is this normal as my car's 10years old? I had two people do an overall check up and both didn't mention anything about it the clutch. I don't know if they missed it or there's nothing to be worried about.

Also, should brake flushing be part of regular maintenance, like oil change?

Thanks!