when the sound is going away thats the gasket expanding under heat. honestly what i would do is pay an exhaust shop to cut the flanges off and weld it together. solve your problem and reduce a pound or so in flange weight even sell them later if you need it. will cost 5$ and a couple of minutes. or even wait 10-15 minutes and have them rid of all the flanges heh
alternative is to buy a gasket from a store for a couple of dollars new bolts (usually exhaust bolts are pretty rusty and need replacement) and do it yourself... would take a few minutes if you have the proper tools (jackstand, wrenches, jack) and you might get a bit dirty... (when there is a leak a lot of carbon will spew out)