There are two places listed in the Shtetlseeker as Grab:
Grab 49°27' N 21°27' E Poland 194.3 miles S of Warszawa Grab 52°01' N 17°43' E Poland 140.1 miles W of Warszawa
Grabie is a bit more fun to look at:
Grabie 49°51' N 20°16' E Poland 168.7 miles S of Warszawa Grabie 49°56' N 19°45' E Poland 168.9 miles SSW of Warszawa Grabie 50°02' N 20°08' E Poland 157.6 miles SSW of Warszawa Grabie 52°02' N 20°13' E Poland 36.4 miles WSW of Warszawa Grabie 52°37' N 20°37' E Poland 30.0 miles NNW of Warszawa Grabie 52°51' N 18°35' E Poland 109.6 miles WNW of Warszawa Grabie Niemieckie 52°26' N 19°44' E Poland 54.9 miles WNW of Warszawa Grabie Nowe 52°21' N 21°19' E Poland 15.0 miles ENE of Warszawa Grabie Polskie 52°27' N 19°46' E Poland 53.8 miles WNW of Warszawa Grabie Stare 52°22' N 21°20' EE M U G Poland 16.2 miles ENE of Warszawa
Since I have no idea who your great grandparents were, it's a little hard to try to find a record online with more information ... like when they arrived in the US, where they went, where they ended up living and other data, which can help us help you.
Research is a process of elimination.The more information you can give us, the more opportunities we have of eliminating the data on wrong people or wrong places.What would be more helpful is knowing what their nationality was.They could have been Polish, but were listed as being from Germany, Russia and Austria because beginning 1772 and up to the end of WW I, Poland was partitioned.Records on Polish immigrants would show them as being from one of the other three countries.