hi i have a problem. recentley my exhaust pipe cracked about 6 inches away from my catco. which i had replaced. o.k here is the deal. my mechanic replaced my catco and he does not weld so he cut off the old one and put the new one on by taking the existing pipe from the muffler and overlapping it onto the new catco pipe then he took a u clamp with 2 bolts on it and put it around the two pipes the he overlapped and tightened the clamp as much as he could.. and it sounded very quiet and normal like if it was a new car. but i recently hit a pot hole and it somehow came loose and sounds like a racing muffler. it dont sound bad but i dont like that sound. it only tends to sound loud at low speeds under 30 mph.. i tried to tighten it as much as i could again but it jus wont go away. then i tried a pipe patch kit from advaned auto and patched up the gaps between the 2 pipes.. yes it worked for about 100 miles then that cracked and now it sounds bad again.. so can i weld them together even tho i put that sh%t on there to attempt to seal it. or do i need awhole new pipe ? thanks

Is this before, or after, the catalytic converter ??

Yeah, they'll just take a wire wheel to the pipes to clean it down to bare metal before welding it on. If the joint is really lopsided or screwed up, they can cut that section out, bend and flare a new piece of pipe and wels that in to connect the cat to the intermediate pipe.