Best answer by Skipping Discs
It's not like a frequency can be copyrighted unless it's arranged in a way. It might sound 'off' having a metronome in a song.
Unless that's what your going for. The young marble giants post punk band used metronomes as their beat. They didn't have a
drummer. They just used a synth/click track in place of a drummer.
I think your in the clear!