Hey there,
Thanks for reaching out about this! We are trying something new with Echo. Let me explain:
5.1 or 2.1 sound systems have a .1 channel that is known as the LFE (low frequency effect) channel. Sounds can specifically be sent to this channel to increase the bass for a given sound. We have been experimenting with adding LFE specific sounds to Echo so this is what you are hearing. The LFE sounds for Echo are mostly limited to when you are playing as her, except for her explosions. There is a bug here - your friendly Echo should not be making these sounds on her explosions. We will fix in the next patch.
It sounds like your subwoofer speaker volume just might be too loud. One clue is that you said having the bass management on causes the bass too be too loud. Bass Management is designed to take bass frequencies that your small speakers can’t reproduce and send it to the subwoofer, which is more capable of reproducing those frequencies.
I would experiment with turning bass management back on, and then using the volume on the subwoofer itself to adjust the bass to be appropriate to how you like it. If you are curious for more information, please do a web search for “calibrating my subwoofer”
Hopefully this fix will make everything you play through your speakers sound better.
I’ll keep an eye on this thread, so please post back to let me know if this helps.