This is killing me guys. 1992 FXDC. I get this "chirping" sound when I let up on the throttle to shift or slow down. It only happens when I am moving along at 20mph or more but it happens every time I let up on throttle quickly. I can't seem to locate what part of the bike it is coming from because I can't get the little bugger to rear it's ugly head when the bike is standing still but my feelings are the belt. Any ideas would be appreciated.

 

I think I had a similar kind of sound on my 94 Heritage it was most notable when I braked, I havent noticed since I changed the oil in the front forks. My guess it was something about when the front forks compressed, not sure if that helps.

 

If you suspect the belt, are things nice and clean back there and is it adjusted properly? I understand that can cause a chirping sound.

 

Loosen the belt to 1in play (10 # force upward bottom of belt cold ) see if this helps HD always run their belt adjustment spec too tight

 

What kind of pipes are yu running? Have heat shields?

 

I had the same thing with my 93 fatboy. The drive pulley on the tranny had come loose. The bolts that hold the lock plate had sheared off and the nut had backed off. The output shaft on the tranny got chewed up a little. I used it as an excuse to put it a 6 speed.

 

Another vote for the final drive belt and or related items....

 

My old "89" bagger did the same thing. If you spray a little water on the belt and take it for a short ride and it stops you will have your answer. I use to spray the belt with some silicone and the chirp would go away for a while.

 

as others have stated it most likley is the final drive belt. check for proper adjustment per the service manual. or clean the belt/ pulleys very well. i have had my belt make the same noise when it was loose, or very dirty from a lot of riding on dirt roads. it is better for the belt to be to loose than to tight

 

I had a noise similar but not identical, which turned out to be a bolt that held the rear sprocket having come loose and rubbing the swing arm. Good luck finding your noise.