20 miles as in MPH or distance? I can't hear much bc of the wind noise above 20mph so Im guessing you're talking about distance. if it's MPH, what is your cadence? when you cleaned perhaps you reinstalled incorrectly if you took out the inner bearing of the jockey wheels. who installed the chain, is it the correct size? how old is your bike? and what does it sound like, a clicking, scraping?