This ASCII 7 (C escape "\a"), which when printed emits a bell sound. The exact sound is terminal dependent, and modern terminals won't use the PC speaker but rather play a sound using the audio hardware (which is required on Macs because they don't have a PC speaker). The bell isn't expected to be emitted often and quickly in series, so depending on the capabilities of the terminal program and the audio hardware, it may go haywire trying to play a more complex/longer sound repeatedly or overlapping (like seeming to lock up or slow down as the audio is queued). Your terminal may be configured to "flash" instead of emitting a sound when ASCII 7 is printed -- this may be implemented as rendering the entire window in reverse video for a short duration. A series of discrete bells played quickly may sound like a tone with a rising pitch. Other terminal oddities could occur if ANSI escape sequences. There are many ANSI escape sequences, for changing colors of text, moving the cursor, changing the typeface, or for querying terminal capabilities or customizing the terminal window title bar, that when printed randomly may make the terminal go haywire.

PC Speaker - https://en.wikipedia.org/wiki/PC_speaker

ANSI Escape Sequences - https://en.wikipedia.org/wiki/ANSI_escape_code