I have an 05 Road King with 13k miles. When I'm in 4th gear I keep hearing a chirping noise this happens when I'm at 2200 to 2500 rpms it goes away at higher and lower rpms and doesn't do it in any other gear. There is no loss of power when this happens. I have a heavy breather kit on it with an after market exhaust and the ecm was reflashed for for the upgrades.
Ive done the usual things checked for loose or rubbing parts.
But if some thing was loose or rubbing the chirpping noise would do it at idle and threw all the gears.
I've taken the bike to my local HD service shop and they say they can't duplicate.
I know that is crap cause I hear it every time I ride also my wife has heard it when she's on the back.
This chirping is driving me crazy.

 

Could it be the rubber mounts for the mufflers in the way back??? never know...shoot a bit of silicone spray in it.... also could be you belt... my belt chirps and i was gonna jack it up today since it will rain....

 

Obviously I can't hear your "chirp" but I can tell ya what mine has just started doing. I hear it only while cruising next to something like a truck or concrete walls of a bridge. Very small chirp but still there. Goes away with accell or decell.
My bike is a 02 FXD carbed bike it did not do this last year. This spring I opened up the carb and rejetted a bit richer and freed the A/F mixture screw to complete a Stage one that wasn't done right by previous owner. So I think it is mixture related just as a carb fart or back fire would be. I noticed the same on my brothers Fatboy after he had some engine work done. He didn't hear it but I did while riding next to his blasting pipes.

 

My old bike had a chirp as i was going down the road. Come to find out the
teeth were gone off the drive belt and every time the bear spot would come
over the small puley it would chirp. It has been a while back and I cant rember
at what speed that I heard it the best.

 

sons 07 Duece had chirp, finally the HD wrench put on some kind of belt dressing on the edge only of the belt. That fixed it. he gave the son some and told him to use sparingly if he needed it again.

 

Thanks for the tips guys.
I will take a peek at the belt after work.