Every bike that I've ever ridden clunked into first gear. My 2007 Fat Boy has almost 5,500 miles on it now, and it's quieted down quite a bit since switching to synthetic oil at the 5,000 mile oil change. It's completely normal. If the noise bothers you, just be glad that you got a '10 instead of an '09. 5th gear in the '07 to '09 range makes a lot of noise as well.
Also, slap some louder pipes on it. The noise from the exhaust will distract your ears from the trans.
thank you people i feel better now. my 2009 lowrider sounded lound sometimes other times no.....i guess it is normal i am happy now thanks i am enjoying the fatboy lo it fits me fine......i am looking at rush black slip ons the stock muffles are to quiet for me lol....the pipes should be black to begin with the chrome satin muffles look stupid....
Try this, when the engine is warmed up hold the clutch in for 10 seconds, shift into first and there will be no clunk.Works with my bike and all other Harleys I have told friends to try it with.