Bicycle Mechanics - Grinding type noise from rear wheel

Newbie here. Took my Hardrock out today for it's christening. Everything was great. No major malfunctions, no wrecks, nothing on the bike brokedown, awesome ride! Came home, started cleaning it and heard strange noise coming from rear wheel. With the bike upside down, I pedal and let the wheel spin freely, there's a 'grinding' kind of metal on metal sound coming from the rear cluster. I took the wheel off and turned the cluster manually and sure enough the sound is coming from the part that the cluster is connected to that makes the wheel spin freely (sorry not up with bike parts terms yet). Anyone have any ideas what might be wrong here? I'm going to take it to the shop for my post first ride adjustment and definitely mention it to them. I just want to learn ahead of time, what the problem might be for my own education. Thanks.

I see you live in FL, did you manage to get some sand in there? A new freewheel or cassette freehub should only be making the clicking ratchet sound when freewheeling.

Good theory, or perhaps the freehub's ratchet or bearing assembly was not properly lubricated during manufacture.

It's possible I got some sand in there but it's not the 'crunchy' sand sound. It's more of a metal scraping on metal sound (like when your car's brake pads are worn out and grinding against the rotor) and it seems to affect the freewheeling (i.e. the wheel doesn't slow down naturally it slows down as the friction increases). It sounds like it's coming from the inside of the middle of the wheel (where the bolt goes through). The clicking ratchet sound is still present as normal.

That sounds like the axle cones somehow got way to tight.? Strange.

someone neglected to pack the bearings?
sounds almost like its dry to me.