Whats up with my pokemon

[Leelue]

ok, now i just got emerald yesterday, and i caught 2 zubat, named them both, and when i went to check thier stats, i noticed that thier voices wer different.
now the first one sounds just like any other zubat, but the other one, Grimm, has the pitch that a normal zubat has when it is knocked out.
so, whats going on here?

[Gogeta904]

It's possible that one was put in the box when its HP was low, but I don't know... that's all I could think of. Maybe your Zubat hit puberty? :]

[Leelue]

HA! maybe, but i need another opinion.