Loud beeping sound under hood

Ok guys, I finally got to work on the dart again. I got the engine warm, pulled the belt and started it, the noise was still there. I then got about 3 foot of heater hose and started trying to pin point where the noise is coming from. It sounds similar to a tea kettle on the stove when it releases steam. With the heater hose I could tell the noise was coming from the carb right around the choke housing. I pulled this little cap off of this vaccum port and the noise stopped. With the cap off you can put your thumb over the port and make the noise start again. I am thinking I have a vaccum leak somewhere else and pulling this cap changes things enough to stop the noise. Any thoughts? Carb gasket? Are there any other gaskets I should check or replace?