So I just bought a 2007 Honda Fit Sport. Everything is great, except the when I try and play audio through AUX, sound only plays through the drivers side speaker, and the passenger speaker makes a crackle humming noise.

I have tried 2 separate audio cables and 2 devices. When using a CD or the Radio, all speakers within the car work.

Would anyone know what the issue is? Could it be a faulty AUX port?

 

Either the AUX port itself or the connection to the back of the head unit.

I had a GD3 and remember the stock head unit. The LCD symbols fade over time and buttons become inoperative.

Given the above and it's already 19 years old, rather than repairing the AUX, you might want to just replace the head unit.

Many aftermarket head units have separate USB access via a cable out the back. One option is to run the USB cable to the glove box and have a flash drive or music player there.

I had a Sony aftermarket (XAV-702) that had two USB cables out the back, one more power than the other for fast charging.