Hello,
 
I started using this 850W G2 along with a brand new rig in July. A couple of days ago I started hearing this high-pitch semi-regular "chirp" or a click while under heavy performance, and after that the sound continued even when idling without any prior heavy performance per session. The sound repeats at almost precisely 1 second intervals often making up to three similar sounds per interval with around ~0.1 seconds between them. The PSU can go sometimes up to ~5 minutes without making this sound, but will eventually continue. The sound is highly audible over my idle system sound and somewhat audible over heavy use.
 
I'm quite certain that this is coming from the PSU (or more precisely from the fan) because when I switch it to Eco mode the sound slows down and finally ceaces entirely. So, is this an indication that my PSU will fail sooner or later (than expected)? Would there be a way to fix the problem? Should I just RMA this? The sound doesn't bother me that much, but the fact that it might affect the longevity of my system does.

Nice rig! It sounds like the fan is the issue to me. Either contact support or start an RMA. At the top of the page are the tabs with support. Good luck, and let us know how it turns out. An RMA should be pretty pain less. :)