My iPhone causes static/scratchy noise in the front left speaker when the iPhone is sending/receiving large amounts of data. The noise is pronounced when the iPhone is in the cubby below the touchscreen, but minimized or eliminated when I am holding the iPhone. The noise occurs even when the speaker is muted. Burlingame SC was not able to fix the issue. Any suggestions? For diagnosis: 5.0 OS, tech, pano, active air, parking sensor, but no sound upgrade, delivered early Sept. 2013.
This isn't a problem with your car. It is caused by the speaker wire picking up the signal from your phone and translating it into sound. It is most common with GSM phones AT&T/T-Mobile. What causes GSM buzz? | Mobile | Geek.com
Verizon's LTE service also has the issue. You can disable LTE on your phone, nor worth it in my opinion.
For what it's worth, my iPhone (AT&T LTE) only does this when it loses LTE (for whatever reason) and drops to Edge (based on GSM). So, even though you have an LTE phone, you might still experience the buzzing sound when your phone drops down to Edge.
I think the issue is more linked to the frequency which it is operating on. From what I've read (not much) the 850mhz bands are the worst. I've recently started getting interference from my iPhone on AT&T when they started up LTE, I believe they refarmed some of their old Edge frequencies in my area.