Do you have any other USB devices that you can test via the problem USB ports?
Is the following link the Quick Start Guide applicable to your microphone?
https://s3.amazonaws.com/cd.bluemic.com/pdf/yeti-nano/Yeti_Nano_QuickStart_REV_C_EN.pdf
If I follow correctly, your earbuds work when plugged into the microphone's headphone output ( audio 3.5mm jack) - correct? And the microphone is plugged into the computer via a USB port - correct?
Try mapping out the problem, for example:
Earbuds to microphone audio 3.5 mm jack = no hiss.
Earbuds to computer USB jack = hiss.
Headphones to microphone 3.5 mm jack = hiss
Headphones to computer USB jack = hiss.
Do other USB peripherals work in the tested USB ports? Likewise map out...