Audio problem: When your Pokemon is low on health it makes a beeping noise. This noise can interfere with Pokemon cries and attack noises (i.e. Kadabra's cry sounds like Ghastly's cry).
Other mistake: If you don't have the Silph Scope, you'll run into GHOSTs at the Pokemon Tower. However, in the middle of the battle, if you see any of your Pokemon's stats, and then return to the battle, the GHOST will be gone and you'll be able to see the real Pokemon behind it.