More than likely you have chosen a latency that is too fast for your computer and soundcard to handle.

Return to the "Audio Settings" menu and increase the "delay" time there.

It is also possible that other processes running on your computer, or even a badly configured or slow graphics card, can affect the performance of PD. Consider running PD with the -rt flag enabled (Linux only!).

This can be done from the command line, or by adding -rt to the "startup flags" under the "Startup" menu.

On Linux or OS X with Jack, it is possible to set the latency of the Jack application to a greater amount and reduce glitches (called "xruns" in Jack) there as well.

this FAQ was originally published under the GPL at Pd's FLOSSmanual