Normally, the road noise is pretty annoying and pretty interfering while motoring along on Interstates at 70 mph. I won’t try to explain it a whole bunch but I noticed that the radio sounds a lot clearer and the road noise a lot less if I also have my Multi Mic remote microphone on and hanging vertically either around my neck in the driver’s seat or around my wife’s neck in the front passenger’s seat. My main thought is just that the Multi Mic in its orientation relative to car speakers happens to be picking up more radio and less road noise than my external HA mics, which are also on at an equal volume setting compared to the streaming volume from the Multi Mic. As I was driving along and the Multi Mic turned itself off due to low battery, I immediately noticed a much greater proportion of road noise when picking up the sound only from my external HA mics. In playing around like this, I also employed the strategy that Mark Chambers suggested to turn up the desirable sound source (the radio volume) and turn down the receiver amplification volume (my HA volume settting) to increase the signal level relative to noise.
Be interesting to hear whether other folks find any merit in employing their remote microphones to help listen to the radio while driving. It seems to make a world of difference for me.