Playing Spotify on my Harley-Davidson speakers using my iPhone 5C and/or Android

[danawood0515]

I have two issues:

1) Volume works sporadically using Spotify with my Harley-Davidson speakers with my with iPhone and Android. I called Apple and they told me to remove the iPhone from its case, which helped with the volume, but still have issue 2, below. I try turning the volume all the way up on using either phone and before I start riding, the volume will be working fine and while riding for a few minutes. Then all of a sudden, the volume will decrease on its own. When I slow down or at a stop, the volume will all of a sudden increase. At other times, the volume works fine during the entire ride. 

2) On the iPhone, sometimes a song will play for a few seconds and then jump to the next song and the next, continuously. This does not happen with the Android.

Note:

I lock both phones, which does not solve either of the above issues.

I do not have either of the above issues using Spotify with my iPod, only with my phones. 

I had my speakers checked at the Harley-Davidson dealership and they are fine. (I also know they work because they work fine with the iPod. But I want to use them with my phones so that I can use Spotify.)

If you have any ideas, please share. Thanks.