Steve G, how is your amp powered ? You may need an additional ground or even a ground loop isolator.

It is powered by a small rechargable battery housed inside the speaker itself. Below is a picture of the speaker I'm using.

Aw yes, the issue very well may be that the speaker and ez-b don't share the same ground reference since they have separate power supplies. If you can find a way (maybe through the charging port) to connect the grounds together the noise is likely to go away.

@Jereime.

Thanks for that. Coming to think of it that does make sense. I will give the grounding a try.

Thanks again.

My plan with the breakout mod is to get an amplified speaker like you have but power it from the bots main battery. Interested to see if you fix it!

No worries Technopro. I'll post an update when I try it.

I experienced a similar annoying hiss when I playing my audio file using the built-in media player. I think that is because there is something wrong with the player. So I download a third-party player to play it. But the same hiss still occurs. I describe this issue to my friend. He suggests that I use an audio editor to remove the noise since the hiss might be from the audio file itself. I employ his recommended Joyoshare Media Cutter. He said that's a reliable audio and video editor that he has been using. Then I try. Luckily, it helps me to eliminate the annoying hiss and won't damage my audio file quality. If anyone who is faced with the same case like me, hope this can be helpful.