Audio beeps in Final Cut Pro

The beeping mean that the audio has not been rendered.
Either render the audio by pressing alt+r or you can turn the beeping off for un rendered audio by going to System settings - playback control - and untick the beep when playing unrendered audio.
Lee

Luis,
what FCP is telling you is that you need to render (can you see the red line running across the top of the timeline?).
(To render>main menu>settings)
Use the manual (main menu> help) to read about rendering and everything you need to know. Simply enter a keyword and go.

What I am also telling you is that mp3 is NOT suitable to edit. It is a delivery compressed format.

Open your audio files with QT and export them as AIFF 48khz then import those into FCP.

G.

Another thing the beeps tell is that the number of tracks of real-time audio playback set in FCP's User Preferences is lower than the demand made by the audio tracks in the Timeline.

Audio effects tax the system with demand for the equivalent CPU power of additional tracks of playback capability beyond the number of tracks in the Timeline.

For example, you might have four tracks of audio during a certain portion of the Timeline, but two of the tracks have audio effects added which require an additional 4 tracks of CPU power. That means, to play that portion back in real-time without rendering, you would need to set the number of RT audio tracks in User Preferences to at least 8.

As you would expect, setting that number higher reduces the CPU power available for video playback.

So, if you're hearing beeps but you really don't want to take the time to render, try changing that setting in User Preferences and see if it allows you to hear your audio.

NOTE: It sometimes might be quicker to render than make that setting change. Audio renders quickly.

FWIW. YMMV.