Reddit reviews Spooky Halloween Sounds

> Around Halloween, it would turn on by itself and play this strange medley of growling, children singing, piano music, etc. It was usually at full volume and would turn off on its own. One time I was able to ask, “Alexa, what’s playing right now?” And the response was that it was “Creepy Halloween Sounds.”

Could be a software "easter egg" (a secret feature put in a piece of software just to amuse people), or an app such as this one (I don't have one of these devices so cannot test if the sounds in this app match what you describe), or even just an ordinary sound file playing. Highly unlikely that this is anything paranormal as the sounds described are very cliche.

> I theorized that maybe a neighbor was playing these sounds at their house nearby (on their porch, or for a Halloween party, etc) and that ours somehow picked up the signal.

This is not technically possible with devices of this kind. This kind of thing used to happen with analog radios, two-way radios, wireless microphones or headphones, and so on. Digital systems such as modern cellphones and WiFi and bluetooth devices cannot "interfere" like this.

> The very last incident was a bit different. My grandma passed away around that time. A couple of days after her passing, the Echo turned on (when I was alone) and started playing “Mandy,” by Boston. I had never heard that song before and had never played it on the Echo. My grandma was the only one who called me Mandy.

That could've been your grandmother, if the paranormal is real. These devices are very sensitive and don't require a loud voice, just a clear one (Google Now on an Android phone can actually be triggered with an electrical signal corresponding to a sound volume that would normally be inaudible, if you give it the right signal), so I imagine that it would be quite easy for spirits to talk to the device (similar to an EVP recorder).