Ah yes, Afghanistan flashback!
When the air traffic controllers at Kandahar blamed the coalition jammers on armoured vehicles coming through the FOB gates, I get calls telling me I need to do something about it because the jamming was my coalition responsibility.
I send a team to investigate and it turns out their radio antenna cables are corroded.
Take a lesson from the war and look at the health of your antenna cable and connections for such activity to be influencing it.
The rest may either fascinate or anaesthetise you:
Radio systems often employ Automatic Gain Control to regulate the volume you hear regardless of signal and noise levels.
AGC is a standard control circuit in car radios and for weak signals it will raise the sensitivity to the point that you think you're hearing more noise in the background of a signal that is otherwise unchanged (it's not the noise that has increased, it's the signal that is very weak in comparison).
When you have very poor signal reception - such as a compromised antenna path to the front end amplifier - any otherwise unnoticeable local car electrical noise is suddenly cutting into a receiver which is operating at maximum sensitivity.
That this is happening when you apply brakes or turn signal further confirms the antenna end of the cable may be compromised.