Sometimes, immediately after tuning in you'll get sound from both sides, but
one side then fades.

This is an artefact of FM stereo tuning on digital tuners: initially, the tuner
quickly locks in on mono audio, then is able to acquire/decode stereo after a
second or two. So the transmitter is in fact only sending audio on one side,
but this gets temporarily copied over to both speakers when first acquiring the

(I had a car audio transmitter that was doing this, but only for songs played from
the SD card -- audio through the line in cable was going through on both channels.
So to verify that the transmitter wasn't actually starting off stereo for those first
few seconds, I did this:

- Play one side only through the line cable
- Tune the station up and down

When first tuning to the one-side-only broadcast, sure enough, I got sound
through both speakers.)