2015 rMBP strange fan noise at low RPM - audio file linked

https://drive.google.com/file/d/0B1qpA4VQILeJaWFjTmVMd2FERmM/view?usp=sharing

I took it in to Genius today and the location was too loud for the tech to hear the fan, so I've since made a recording. Is the sound typical or normal? Do I need to take it back and get it checked out again?

The .3GP audio file linked above is a recording of the fan noise I'm hearing. I placed my phone right up to the fan vent to capture the audio, so it likely appears far louder than it really is. The sputtering sound is only apparent when the fan runs at low RPMs. If the laptop comes under heavy load and the fan kicks in all the way, there's no apparent sputtering.

Thanks