usb wall chargers for both sandisk and i-home speaker

SanDisk MP3 players Sansa® Clip | Sansa® Clip+
1

i have an i-home mirco speaker hooked to my sandisk clip+.

Both the clip+ and i-home are constantly being charged with dedicated usb wall charger outlets,i.e. one charger for the clip+ and one charger for the i-home.  All is OK.

When I try to use a single wall charger with dual usb ports, I end up getting a constant clicking sound from the speaker and no music.  The wall charger is rated at 3.1 amp which is more that the single wall chargers.

What gives?  The same thing happened on another clip+ so it seems inherent in running both the speaker and the clip+ off of one wall charger.

2

The player and the charger use very different grounds.  This is fine normally, but if you hook up the charger to the player and the speaker at the same time, you short the clip ground (which is probably about 1 Volt) to the speaker ground, which is probably hooked up the charger ground.  Hence you create a short circuit.  The player then disconnects the power to its analog out to avoid vaporizing itself.  

A coupling capacitor or isolation transformer will break the loop.