I have had several issues trying to get my 16.4.2 properly working with my 2011 iMac and Pro Tools. Every 20 to 30 seconds there is a loud pair of pops that show up on the Gain Reduction meter. The meter spikes all the way from -1 to -21. It doesnt matter if i have the tracks record enabled, or have the faders on, or gain on. It seems the issue persists any time i have the board plugged in to my mac and my monitors (KRK Rokit 6- in the main output with balanced 1/4 line ins). Occasionally the error message AAE-6101 will show but it still pops without that error message. I have tried a few things that the avid website suggested for this error message but they did not resolve my issue.