Cheers to all! Here is whats happening: my 3 y.o. 15 MBP is connected to external speakers (Bose MusicMonitor) and every time there is a sound, any system sound, say an email in, a volume chirp, or a Skype chirp, anything at all, I hear an audible POP, before hearing the actual sound, in fact the POP sort of overlays the sound. I hear the second POP sometimes, after the sound has sounded, so to speak, and sometimes the second one does not happen at all. To me it reminds me of the Pioneer Amp my dad used to have in the 70's, when you first turn that thing on, it would produce an audible POP. So, back to to this, it sounds like an amplifier POP by being awaken by the system, and I'm inclined to think it is the MBP's audio "amplifier" on its board. Oh, btw, both the speakers and the MBP's volume is set to low. Thanks in advance!