I've noticed a significant difference in not only loudness, but also quality when using iPhone thru Bluetooth. I much prefer using USB cord for a couple reasons: sound quality is way better, it charges my phone, the screen album on the display. However, I've just recently noticed two issues that seem to have begun. One is that I cannot forward or replay a song, only volume control. Second, every single time I shut the bike off and restart it, I have to reset the volume speed control setting.
I actually stumbled across this feature one day, when I felt like I just wasn't getting the same quality sound at speed, and when I went to the volume speed setting, lowered it a notch from the "4" settings, then put it back up to the 4th bar, the amps really kicked in when I started moving again!! The sound is incredible, but as I said, once I stop and chit off the bike, I have to go through the process again. Not a big deal, more of a pain. The ability to skip songs or repeat, now that's a problem!! Any ideas???