Signs of trouble.

The cause of Whitney Houston's shocking Saturday death at age 48 has yet to be determined, but the "Saving All My Love for You" singer, who struggled with drug and alcohol abuse in her later life, made a bizarre appearance just two evenings before.

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At a pre-Grammys party at Tru Hollywood Thursday evening, the beloved Grammy-winning singer seemed "wasted" and "moody" as she exited the club past midnight, according to a witness. "She reacted angrily to the security guards trying to get her into her car...and started cussing them out."

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Although the superstar smiled when fans approached her for autographs, "she would get moody again in a split second," the observer says. "It was sad because her fans noticed that she was really shaky as she left the venue. She definitely was not in control of herself."

Yet, the next day, doing a sound check for a planned performance at mentor Clive Davis' annual Grammys party, Houston "was fine" doing a sound check, according to another source. "She was present and ready...She had water to keep her vocals clear, and was trying to not smoke."

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Davis, who discovered Houston singing at an NYC club when she was just 20 years old and quickly gave her a record deal, has canceled his annual bash in light of Houston's death. "He's not having it anymore," his label confirmed to "It's been canceled. Very unfortunate."

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