I’ve seen several complaints about this.
When Alexa completes a task, it gives a notification sound. It used ro be a coupke of innocuous tones. Then they added a sound that sounds like a ghost starting a car! Really heavy on the bass so it’s jarring.
Now there are also animal noises, birds, etc.
I HATE THEM.
And,there is no way to change these sounds or turn them off!

Who decided to do this? Why?
Was there no approval or oversight?
Seriously! And no way to change them?

As long as I’m complaining, there are several other bothersome changes. My Echo Show(s) start randomly playing commercials, for example.
I use my Echo Shows as a click as well. But it’s decided to jyst show photos without the clock, and again, no way to change that.

Would a factory reset help? Or is that a temporary fix until the next forced update?

I’ve outlined that in the rant above.