I know, it`s an exhaust leak, right? What to do now?

I have a 3`` exit y-pipe that connects to my 3.1`` JIC ti single. New gaskets. The car runs smooth and hard. Since the y-pipe is newish I decided to check on it and noticed there was some carbon on the bottom of the flange after driving it 300 miles or so with this setup. A whoosh/hiss ONLY above 3-4k and under heavy throttle also made a strong leak argument. This hiss was definitely coming from the underside middle of the car. So...

I cranked down the bolts bigtime (got maybe a 1/15th or 20th of a turn more, which seemed substantial considering the big torque I applied) and expected some change. Nope. Same hiss as before when I`m on it in 3rd accelerating on the hwy (windows up to hear it clearly).

I`ve read posts about getting an exhaust welded. There have also been posts about using some high temp gasket putty.

How much would a weld for one connection cost at a shop? Would you do the weld , the gasket sealer, or ?