I wanted to have Bluetooth with my stock head unit so I grabbed an adapter and plugged it into the aux in. There was a lot of interference so I added a ground loop isolator.
Anker SoundSync Drive Bluetooth 4.0 Car Receiver, Wireless Phone Call & Music Streaming Car Kit with Built-in Mic, Music Streaming, Echo and Noise Reduction, Multi-Point Access, 3.5mm Aux Cable
https://www.amazon.com/dp/B0176G5TRO..._njEvzbN5QN48M
AUKEY*Ground*Loop*Noise*Isolator*for Car Stereo*Systems and Home Audio Systems, 3.5mm Audio Cable Included
https://www.amazon.com/dp/B01L1NP7YI..._8jEvzbBG375J4