Say, what’s Amy Heidemann doing on the cover of Rolling Stone? The pretty, pompadour-sporting half of Karmin — the YouTube sensation turned chart-topping pop duo formed at Berklee — is on this month’s cover because her fans want her there. That’s right, Karmin was chosen by folks who voted in the mag’s “Women Who Rock” contest. Nearly 1 million votes were cast, with Karmin finishing just ahead of Rita Ora. (The issue hits stands Friday.) The band — the other half is Heidemann’s fiance Nick Noonan — will perform on TV’s “Dancing With the Stars” Oct. 9.