Answer:
I am the noblest musical instrument
I am an odd number. Take away a letter and I become even. What number am I?
I am taken from a mine and shut in a wooden case from which I am never released. Yet I am used by almost everybody. What am I?
I go in hard, come out soft. Blow me hard and I'll make a pop. What am I?
The person who makes me doesn't need me. The person who buys me doesn't use me. The person who uses me doesn't know it. What am I?
No matter how little or how much you use me, you change me every month.