exhaust chirp

[70Bonnie]

Been lurking around for a while and now I need an opinion so I signed up. :-) 1970 Bonneville, no balance pipe, Dunstall megaphone copies, no baffles. Head has been decked and I am using a thicker head gasket. (.080" copper)  Plug looks good, nice tan colour. The right side exhaust has a chirping/whistling sound as it winds down after throttle. Left side is fine.  I wear earplugs so I hadn't noticed it. A buddy riding behind me heard it and let me know. I checked the tappet clearance in the right exhaust and it was tight. Reset to recommended .004 and no change. There is no noticeable loss in power/compression. No strange sound when listening to the engine, it's only noticeable at the muffler. All opinions appreciated.

[R]

Are your exhausts and mufflers identical side to side ?
Can you swap the Dunstalls side to side, see if it changes side ?

A lot of exhausts chirp/whistle on the overrun - Norton Commandos had those famous 'tweety' mufflers, aka as peashooters.

Although not sure that Dunstalls would fall into that category.
Not something partly blocking one inside anywhere, is there ?

Is is pulling strongly on both cylinders, carbs synchronised, one cylinder is not doing more of the work ?  Will it idle on one cylinder, each cylinder in turn ? (don't do this if you have electronic ignition).

[70Bonnie]

It's a stumper. Same pipes and mufflers. Even swapped in a pair of real Dunstalls off my '72, no change. The chirpy side doesn't idle quite as well as the other. I did a check by squirting carb cleaner through and it doesn't look blocked. It  pulls well when the throttle is opened, carbs are synched.  I haven't swapped out the pipe though. Could unscrew the exhaust pipe adapter and swap a push-in just to test and see if that solves it. Then, as you suggested,  I'll know if it something in the pipe is causing it. Old school....I like my points.  LOL

[Matt]

I would whip the head off and have a peek my VB had that noise and it turned out to be head gasket failure.

[rogerwilko]

Headgasket noise is most noticeable when under power not over run.

[70Bonnie]

Head gasket is new, I put it on. No Oil leaks at the gasket. Couldn't get a fit with the push in pipe so I abandoned that idea. I ran it a bit with no pipe and couldn't notice any mechanical noise. I have to go back to it being some irregularity in the pipe. Sound plausible?

[Rex]

Does to me.
Just one of those idiosyncrasies of old bikes, allied to the weird effects of harmonics, etc.
 Goldie owners used to make a big thing about the over-run twitter, as do Beetle owners...