On the eve of the 51st Grammy Awards, most of the show's performers were keeping it loose in rehearsals.

Sir Paul McCartney played a couple of covers and indulged the small crowd on hand in a lengthy jam, while Coldplay frontman Chris Martin cracked jokes and hung around afterwards to pose for pictures the night before Sunday's show.

McCartney's band tossed off a cover of Fleetwood Mac's "Hi Ho Silver" before playing "Let Me Roll It," a track he recorded while with Wings.

Then, keyed by the aggressive drumming of Foo Fighters frontman Dave Grohl, he followed with a blistering version of the Beatles' "I Saw Her Standing There" - the song McCartney will actually perform at the show.

He seemed to enjoy interacting with the crowd, too. After the band had repeated the same measure several times for soundcheck purposes, he broke the monotony by addressing the audience.

"We're going to do this again and again, but we would like you to keep up your level of enthusiasm," he said with a smile. When the crowd responded by clapping, he added: "That was better than I expected."

Martin was similarly good-humoured in his dealings with the crowd. Sitting at a piano on a circular stage in the middle of the Staples Center auditorium, he noodled around on the keys while waiting for the go-ahead from producers.

"I'm just trying to show off my skills," said Martin, whose band has seven nominations - second only to New Orleans rapper Lil Wayne.

He was joined at the piano by New York rapper Jay-Z, who dropped a verse then faded away as Martin joined his Coldplay bandmates onstage for "Viva La Vida."

Though Martin was troubled by the mix - "sounds very strange," he said - he kept the session casual.

"Next, on 'American Idol,"' he said in faux theatrical voice as he sat down at the piano, before adding: "I'd never make it on 'American Idol' - I don't have the cheekbones."

Later, he flubbed his cue by talking through his introduction.

"Can you do the last bit again, mate?" he asked. "I'm sorry, I (screwed) up."

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