Popping noise ?

Use slip-edits to hide the transitions.
 
The popping you're hearing is what a sudden level change sounds like. If you zoom in close on the clip you'll see that the waveform doesn't start at zero, but at some higher value. That's always going to make a clicking or popping sound. A slip-edit can be used to fade in the clip and avoid that pop. The fade-in doesn't have to be very long; a few milliseconds will do.

FYI:
 
Large Buffer Number = smooth playback and higher latency.
Small Buffer Number = low latency, which can cause pops, clicks, and glitches.
 
If it just happens at the front of a track, drag it over to avoid the pop, or split and cut it out.
If it constantly is happening, try raising your buffer. You should be ok with up to a 10 to 12 mill latency.