The Bible doesn't state it directly, but Noah sent out the raven (a carrion-eater) in order to ascertain that predatory mammals would be able to survive on Earth — that is, until at least some of the land had been exposed, along with its plethora of corpses. He later sent out the dove to check for fertile land that would support herbivores and humans.
What if our Noah only sent the grackle?
As a mortician in his earlier days, Raymond would have direct access to the dead. It'd be rather easy to pass off ashes for a cremated body, since allowing a family to watch a body burn in real time is uncommon (even when they're permitted to see the cremation machine at work). We know that Noah can eat dead bodies and still be sated — Justin is proof enough, unless Noah feeds on souls rather than flesh.
All this can be combined to create a timeline of sordid events — a starving, heathenish Noah may have resorted to eating out of coffins to keep from murdering people, and Raymond could have been convinced (perhaps even threatened) into obliging. With this in mind, it's not difficult to envision how the two of them fell out, and why Raymond would want to sabotage Noah's priestly position.
Nobody else was seen living at the motel aside from No while Christopher was still around, Crystal has repeatedly complained about the fact that she works alone for every single shift, and the Home Depot noticeably lacks any regular employees and just has cultists of the Home Depot God. Each of these could be attributed to the disappearance of previous tenants/employees, given that it's unusual for stores to only have a single employee or motels to have a single occupant.
