The spell does need to be cast from your hand, if it gets cast from anywhere else (like with Cascade, for example), Rebound wont trigger, and so to the graveyard with the spell

Adventurer's Airship Angel of the Ruins Anvil of Bogardan Architects of Will Argentum Masticore Arm-Mounted Anchor Armix, Filigree Thrasher Ashnod's Transmogrant Assassin Gauntlet Bag of Holding Big Wheel Blood Fountain Blood Servitor Bloodsoaked Altar Bloodthorn Flail Blurry Beeble Bomat Courier Boosted Sloop Brass's Tunnel-Grinder Ceremonial Knife Chandra's Regulator Clamorous Ironclad Clockwork Avian Clockwork Beast Collector's Vault Colossus of the Blood Age Containment Construct Coral Helm Cryptcaller Chariot Currency Converter Cursed Rack Cyclonus, the Saboteur Daily Bugle Newspaper Data Scrubber Deal Broker Detention Chariot Diamond Lion Dictation Quillograph Disrupting Scepter Dodecapod Draconian Cylix Elaborate Firecannon Emmessi Tome Esper Sojourners Everythingamajig Flamewar, Brash Veteran Flowstone Sculpture Flying Drone Fodder Tosser Gastal Thrillroller Gate to the Afterlife Glass-Cast Heart Glassdust Hulk Grafted Skullcap Great Gilded Boat Grimoire of the Dead Harnfel, Horn of Bounty Hazoret's Monument Heirloom Mirror Hollow One Indatha Crystal Ironhoof Boar Izzet Keyrune Jackdaw Jalum Tome Jandor's Ring Junk Golem Ketria Crystal Key to the City Key to the Side-Door Knowledge Vault

Does Populate Triggers ETBs
Right now, the most expensive card on the drop list is Stifle, weighing in at about $14
Im focusing on cards that trigger when they enter rather than when another card enters
If you're relatively new and have yet to experience it, trust me, it's only a matter of time