Sinn joined The Distillers after their first album had been made. At the time he only played guitar, but he learned to play the bass parts on their previous album in four days and was asked to join the band after he auditioned. He appeared on the group's second and third albums. The band experienced some turmoil in 2005, and Sinn announced that he had left the band on his MySpace page in August of that year.
After leaving The Distillers, Sinn was recruited by Blink-182 member Tom DeLonge to join his new project, Angels & Airwaves. He played bass on the band's 2006 release We Don't Need to Whisper. However, in April 2007, rumors spread that Sinn had left Angels & Airwaves due to difficulties with the rest of the band. The reasons of his dismissal are still unknown to the fans as no further announcements have been made by the rest of the band. In May, these rumors were confirmed by Sinn. Soon after the announcement of the departure, Sinn posted on deathouse.org that he would be auctioning off items associated with AVA, including a Tom DeLonge signature guitar that DeLonge had given him.