You should definitely use the forum's "search" function to look through prior posts -- your problem is a common one.
Clicks and pops are often caused by setting your sound card's buffer size too low.
What are your sample rate / buffer size / samples per buffer / etc. sound card numbers?
This web page is talking about different hardware, but the concepts are applicable here, too:
What does Override Internal Buffer Size do?Some other thoughts: does the sample rate that you've selected in Giga's Configuration Manager match the sample rate that you've selected in whatever app accompanies your sound card?
The "Override Internal Buffer Size" setting is found in Performer or Digital Performer's Configure Hardware Driver dialog box when the Audio System is set to use the built in jacks on the mac. MAS defaults to an internal buffer size setting of 1024 samples per buffer. This buffer size setting can be adjusted to another setting other than the default 1024 samples. Lowering the buffer size can reduce latency on faster processors. However, the payoff of lower latency will be slower response in Digital Performer. Realistic override settings are 512 or above. Alternately, if you encounter audible pops, clicks or distortion in your audio, you may want to increase the buffer size. You do not want to set a buffer larger than the default.
Are you overloading your CPU? Keep an eye on the CPU meter as you load/launch/play the piano...