I hear that there is some couch located on the overpass near Greygarden. Where is it? At the very top of the overpass? Or is it somewhere else? I need to know because I know settlers wander there.

Top level. They are sometimes spawned in the air and drop down.

There's a vertibird wreck up there on the side of the upper road deck also, just east of greygarden. Those often have PA nearby- anybody know if it's accessible?

It seems to be a tip for finding power armor if you find an old crashed Vertibird, there is usually power armor nearby (hint, hint )......the upper road deck can be accessed via a lift.

Why don't you go an look?

I scrapped that dang thing as quickly as I could. I don't know if it stops them spawning there, but at least they can't hang around up there any more.

In Case You Didn't Know Dept: At Graygardens, part of the overpass overhangs the "green zone" that constitutes the GRaygardens settlement site. With the obvious exception of water pumps and plants, most anything can be built up there.