Midi track creates occasional pops and cracks to audio with Persian Santoor sound

When playing or recording midi with Persian Santoor sound it creates occasional pops and cracks to audio. This problem seems to appear only with this particular midi sound since changing the sound to any other makes the pops to disappear. What is also really weird is that the pops come out only from the left channel! I've tried listening through different speakers and headphones, with or without my USB audio interface (M-audio Fast Track C400) with no difference. The pops and cracks also appear in the bounced audio.

I'm using Logic Pro X (Version 10.1.1) on a MacBook Pro late 2011 with OS X Yosemite (10.10.4). The same problem also occurs with my second computer: Mac mini late 2012 with OS X Yosemite (10.10.4). Increasing I/O Buffering size didn't make any difference.

Please help! 😕