i have an 88 13b non turbo stock exhaust manifold with the first two pre cats removed and i only have the main cat with borla exhaust from cat back. all gastkets replaced except i haven't removed the manifold from the engine that gasket is original. it sounds fine but i still hear a popping or exhaust leak at the manifold or are the reactive stock manifolds normaly loud? thanks for your time

 

welcome to the forum. did it make the noise before you got rid of the precats?? if not i would think that the (downpipe) isnt sitting properly against the maifold or the cat. thats my best guees also might be your aux port pipe not being tight or rusting through i had that problem too.
hope this helps