Rieflin began his professional career in his hometown of Seattle. In 1975, he was in The Telepaths, a band which played backup for a couple of live gigs by the pre-The Screamers band The Tupperwares. He played drums for The Blackouts starting in 1979. His bandmates included his brother Raymond, Paul Barker, Roland Barker and Erich Werner. Eventually that band dissolved and Paul Barker joined the nascent Ministry. Rieflin's earliest collaboration with Al Jourgensen was on the second single by the Revolting Cocks, You Often Forget. Later, he participated in the creation of Ministry's ground-breaking album The Land of Rape and Honey. He was noted for his performance in the live video In Case You Didn't Feel Like Showing Up (Live) (alongside fellow drummer Martin Atkins). His work with Ministry and its side projects lasted through to the mid-Nineties, though he notes that he was never credited as a member of Ministry proper, always as an "other" musician. Therefore, when he parted ways with the band during the Filth Pig sessions, he did not really quit since he was never an official member.
Rieflin helped Atkins kick off Pigface, the industrial collective that would grow to incorporate hundreds of artists, formed a friendship with labelmateChris Connelly and founded First World Music. Like Connelly, Rieflin's work has grown beyond his industrial roots. They have collaborated on several recordings; two in particular, The Ultimate Seaside Companion (as "The Bells") and Largo, showcase Rieflin's frequently overlooked keyboard skills.
Rieflin appeared on all KMFDM records released from 1995–2003 as a drummer, programmer, vocalist and keyboardist. He toured with the band as a bassist in 2002 in support of its comeback album, Attak and performed on the 2011 KMFDM album, WTF?!.
He also drummed for McCaughey's band, The Minus 5, which occasionally included guitarist Peter Buck. Eventually Buck offered Rieflin the opportunity to sit in with R.E.M., who were missing a permanent drummer since the 1997 departure of Bill Berry. The band gave him the live drummer slot in its 2003 tour. They later announced that Rieflin would fill the role indefinitely, though once again as a hired musician rather than as an official member. In recordings, Rieflin also contributed bouzouki, keyboards and guitars to the group, serving as an auxiliary member until R.E.M. disbanded in 2011.
Rieflin formed an experimental ensemble under the name Slow Music in 2005 (including Fripp and Buck) in which he plays synthesizers rather than drums. As the name suggests, its approach is geared toward the musicians leaving space for each other and doing a lot with few notes. All performances are improvised. The group played a small handful of live dates in 2005 and 2006 and went inactive for several years.
Rieflin is involved in a music collaboration project entitled The Humans, which consists of him, Chris Wong, Robert Fripp and Toyah Willcox. The band performed a series of live dates in Estonia in Autumn 2007 and 2009, and released their debut album We are the Humans on May 1, 2009. Another album came in 2013, followed by a small series of double-bill shows with Slow Music in spring of 2014.