Spencer -- GaGa Makes My Ears Bleed!!!

With LC out of the picture, Heidi and Spencer are waging a brand new celebrity war -- on Lady GaGa.

Speidi: Click to watch
On his way out of the Star Magazine Young Hollywood party last night, Spencer ripped on LGG's music, claiming he had to "save my ears from Lady Gaga" -- but judging by who he went home with ... he's heard worse.

The story behind the beef is this: Gaga wrote a song called "Fashion" that both she and Heidi recorded. Guess whose version people preferred ...