My 2010 g37x randomly started doing this about a week ago now, i only realized it because i heard the alarming noise when pulling through a drive through! Pretty much the noise only happens when the rpms drop down to 500 and stay there for a few seconds and the only time that really happens is if im sitting in drive with the A/C off at a dead stop, this happens in reverse as well and sometimes park although its harder to replicate in park and neutral im guessing because the rpms aren't dropping as low. I suspect it may be something to do with the belt or idler pulley something of that matter although i have been told it may be a vacuum leak which i cant seem to find one.

Attached is a sound clip of the noise, Its a high pitch constant noise that almost sounds like a beep or a buzz that's coming from the engine bay very very annoying.

 

Quality sound clip https://imgur.com/gallery/9bUJrNU