Pandora Media ( P ) shares was down more than 4% in midday trading Monday on new research showing a lower September advertising load and continued threat from Apple 's ( AAPL ) new iTunes Radio. "We have trialed iTunes extensively and continue to see it as a credible threat," wrote Canacord Genuity analyst Michael Graham, "although we expect limited impact to Pandora's September and October listener metrics." Graham maintained a buy rating on Pandora stock and boosted his price target to 30 from 25, saying that the company's Q3 is still "tracking well" despite the challenge from Apple. Pandora and iTunes Radio both offer free ad-supported Internet radio. Graham and his team each month listen to Pandora to figure out how many ads are being served up each hour, and they found that the ad load dropped to an average of five spots per hour in September from 5.7 in August and 5.2 in July, Graham wrote in a research note on Monday.