I bought a cheap $40 radio for my truck since the factory radio was on it's last leg. No iPhone control. Just a auxiliary and USB port.
For whatever reason, whenever I use the 3.5mm to 3.5mm adapter, I always get some sort of static/ clicky interference in the speakers. I imagine it's my phone emitting some sort of signal. I've used different cables with the same results. Makes listening to it pointless most of the time so honestly I've given up for now. FWIW, it works fine in say a 2016 model vehicle with an auxiliary port built into the factory system.
What could be causing this? I am not too "car audio" savvy. I have a nice Kenwood in my Jeep that was a (at it's time: 2010) flagship model with iPhone controls. No issues whatsoever even with my newer iPhone 6S.
03 Jeep WJ 4.0 197k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 170k M1 0w40 Mann HU818X
97 Chevy Blazer 4.3 142k Rotella T5 10w30 Fram TG3980