I have a 1999 FXSTC (basically still stock) that produces an annoying chirp in the following situations when riding along at 50-60 mph: pull in clutch and release (chirp); release throttle (chirp). However, engage front brake (no chirp). So it doesn't appear to be related to the front suspension. Bike was just serviced and all cables look good. Ideas?

 

A blown head gasket will produce "chirps" like this.

 

I'm battling a chirp on my 98 Fatboy as well. There are a lot of threads on the subject. Mine works in the opposite, it only chirps when I throttle up, but, not on decel or letting the clutch out. From what I gather you problem sounds like the drive belt is a little loose. You can do a simple test to check if it is your drive belt by rubbing some soap or parafin wax on the outside edge of the belt. This will quiet it down immediately if it is your belt. Read the threads and try your options. I corrected mine for a while but it's come back, so I think I have to realign the rear end. Good Luck.

 

I have been told the chirp on my 90 Heritage is the Manuki carb. Hard to hear it without the windshield. I can see where it will get on your last nerve.

 

My bike will "chirp" like you describe if the belt is a bit loose. Check your belt adjustment before you do anything else. MY belt will chirp when chopping the throttle if it's loose, and squeal if it's too tight.

It's worse starting out on a cold morning, as the belt is looser when cold, and tends to tighten as the bike warms up.

 

It is definitely a belt issue.
Quite common.
Ensure belt(and pulley) is well cleaned, with mild soapy water and an old toothbrush, or the like.
Follow this with correct adjustment.

 

If you can't clear up the chirp with a good cleaning or a little silicon spray on the belt, you may need to check your transmission drive pulley. Mine had a 1/4" groove worn in it. A new pulley made the chirp go away.

 

Should cleaning and adjustment not suffice, this,as well as the pulley being loose, is quite reasonable to consider.

 

Not to steal the OP issue, but my chirp was at the tailpipe(s) rubber mount(s) & needed to silicone to prevent the noise.

 

Now that you mention it... I have not noticed my chirp since I replaced the Mikuni with a stock CV carb.