Knudsen was born in Le Mars, Iowa. He began drumming while attending Princeton High School in Princeton, Illinois, where he graduated in 1966. After short stints playing in a clubband and the Blind Joe Mendlebaum Blues Band, he became the drummer for organist/vocalist Lee Michaels. He played in The Hoodoo Rhythm Devils from late 1972 through mid 1973. He never did any formal studio recording with them, but recorded a live Texas Special on KSAN-FM in San Francisco with the Hoodoos and Johnny Winter. His big break came in 1974 when he was invited to join The Doobie Brothers, replacing the departing Michael Hossack. Knudsen joined the band during the recording of the 1974 Top 10 platinum album, What Were Once Vices Are Now Habits. He made his recording debut with the Doobies on What Were Once Vices Are Now Habits in 1974, performing backing vocals over instrumental tracks that included Hossack. Knudsen did not get behind the drum kit in the recording studio until Stampede in 1975. Knudsen was co-drummer with John Hartman and later Chet McCracken until the Doobies disbanded in 1982. His contribution to the group's vocal harmonies in the studio and in concert was as crucial as his drumming. After the Doobies disbanded in 1982, Knudsen and fellow Doobie John McFee formed the country rock band Southern Pacific. The group was successful in the country charts but disbanded in the early 1990s. By then the two men had formed a writing partnership and despite not rejoining the group at that time, co-wrote the song Time Is Here And Gone with Doobies' percussionist Bobby LaKind, featured on the Doobies reunion album Cycles in 1989. Knudsen organized a one-off Doobies reunion in 1987 to raise funds for the National Veterans Foundation. After Southern Pacific folded, both he and McFee rejoined the Doobie Brothers on a full-time basis in 1993. Ironically, Knudsen found himself drumming alongside Michael Hossack, whom he had replaced all those years ago. Of the multiple pairings of Doobie Brothers drummers over the decades, Knudsen's time-keeping partnership with Hossack lasted the longest. He featured prominently as a songwriter on the albumSibling Rivalry, which was, at the time, only the band's third studio album since reuniting. He also featured on the albums , and Live at Wolf Trap. In 2005 he played drums on Emmylou HarrisShores Of White Sand off the All I Intend To Be record. Though Knudsen was a frequent backing vocalist for the Doobie Brothers, he did not sing lead on many released Doobies tracks. On "Double Dealin' Four Flusher" he is heard trading brief lead vocal lines with Pat Simmons and Tom Johnston. Knudsen can also be heard singing lead on songs from the 1982 Doobie Brothers Farewell Tour. Sibling Rivalry features two later, and very different sounding, Knudsen lead vocals. Knudsen died of pneumonia in Kentfield, California, at the age of 56. He was living in Northern California with his wife, Kate, and his daughter Dayna at the time of his death.
