My Carburetor is singing the blues!!

Sounds a little like a vacuum leak. Do you see any discolorations around the carb base? Like it was leaking a little gas and then drying.
I had something similar happen, the carb gasket acted like a reed and would give a high pitched squeal.

That's so funny! A few weeks ago I kept hearing this low air horn noise when I slowed down. It finally got loud enough that I thought I may have a low current short in my horn, but all the honking in the world wouldn't make it go away. Turned out the top tank on my rad had seperated from the core and was acting exactly like the pressurized brass horn on my sailboat! It wasn't hot enough to overheat so there wasn't any steam. I actually laughed when I opened the hood and discovered what it was.