Pandora Media Inc will increase fees for its ad-free service by $1 a month to almost $5 a month in May, a move to cover the rising cost of licensing tunes that may annoy some longtime fans of the popular music-streaming service. The company, which streams music from virtual radio stations to mobile devices such as Apple Inc’s iPhone or Google Android smartphones, said in a Tuesday blogpost that royalties paid to artists had risen 53 percent over the past five years and will rise another 9 percent in 2015. The increase of $1 to $4.99 a month takes effect for new subscribers in May. Existing monthly subscribers will not be forced to accept the higher charges for now, it said without elaborating. Yearly subscribers paying $36 a year currently will move to a monthly, “loyalty” $3.99 plan once their memberships expire.