When I use punch in/out for audio track recording, there are often a 'click' or strange sound at the punch in/out points. Why? How can I eliminate this problem? Any help would be appreciated.

The 'click'/strange sound appears when I listen to the playback.

Clicks may occur if (A) the load on your system is too high or (B) the recorded waveform does not start at a zero crossing ... for (A) you could try to increase your ASIO buffer or disable some FX, for (B) you could fade in the clip, a very short fade will do ... I suspect it's (B)

Yeah, I'd start by drawing in some fades and see if that takes care of the clicks.

Thanks for your suggestion. I will try the fade in.