Whitney Houston 'Partied Heavily' the Night Before She Died

Whitney Houston "partied heavily" at the Beverly Hilton hotel with a group of friends ... hotel staff tell TMZ.

We're told Whitney and her friends were in the bar for a time and the group was drinking and very loud. Our sources say even though the hotel is busy with all the Grammy festivities, Whitney and her group stood out because they were so boisterous.

Again, it's too early to know what caused her death.