Audio clicks when playback is stopped.

Question

In the process of recording a couple of bass guitars that were Keymapped into sampler instruments, I noticed some strange audio behavior. While playing the new sampler instruments, finger lift off from my MIDI guitar controller was causing a clicking or sucking sound each and every time. (The recorded notes in Logic were allowed to decay naturally and the samples were not looped.)
So I went to the recording in Logic and sure enough, hitting the space bar or numerical decimal would elicit a click when stopping playback. A quick test recording was completed in Digital Performer with the same result. Also a quick test in Logic with the smallest and largest i/O settings. Same problem.
Recording signal into the Mac via Built-in Line input also produces the same clicking. So that removes suspicion for my interface (828mkll with Black Lion mod) which has been a rock-solid performer.
I have 5 GB of Ram. OSX10.5.5, 7200 RPM sata drives, etc.
Is this some sort of core audio issue?
What to do???

Answer 1

Ok, I recorded each bass chromatically into Logic in real time (not triggering samples via MIDI).
The resulting audio files were opened in Keymap to be converted to an EXS24 sampler instruments.
The lift off clicking noise occurs with both basses but not with factory sampler instruments I play with the Godin LGX-SA.
The point about the spacebar or numerical pad decimal point is that when I use either of these to stop/start playback of the original audio file in Logic, clicking occurs. Uninterrupted audio playback is fine. Interrupted playback causes clicking which should not occur. While attempting to problem solve the funny lift off noise while playing the sampler instruments, I noticed that interrupting playback of the original recording in Logic caused clicking.
I recorded the same bass guitars into DP (not MIDI-triggered samples) through the same interface with the same clicking problem when audio file playback is stopped via the spacebar or DP keyboard commands.
So there are no MIDI messages involved here. The point of mentioning the sampler instruments is just that that was the when I noticed the audio problem. For simplicity sake, if we leave sampler instruments out of the discussion, I am still left with some sort of audio problem.
The same basses played and recorded via Built-in Line input causes the same clicking to occur during interrupted played back.
Somehow. the noise that occurs with finger release from the fretboard is related to the problem with the audio clicking when stopped during playback. Meaning that the audio file is corrupt in some way.
I followed your suggestion of unchecking both play tickboxes in the Sound Effects tab of the Sound preference. The problem still exits.
So in summary, at this time, I cannot record audio into my Mac without some sort of clicking problem when stopping playback. Audio that I record then causes some strange lift off noise or click when played as a sampler instrument. The base problem is that something goes wrong when audio is recorded into my Mac.