I am using Sonic Port VX, with my iPhone7. This issue is very annoying.... However, I don't experience this same thing when using with iPad Air (first edition)....
Recently updated my iPhone7 to 11.0.3, seems the issue is getting resolved. I am plugging my PC to Port VX as input, then connect to my iPhone7, while use headphone out to an external speaker. Playing music in PC for ~10mins, only heard 1 clicking (not sure if that's from the music itself =P).
For those who have this issue, you may try updating to the latest iOS.