Chevrolet - Blazer :: 1999 - Exhaust Noise At Cold Start And Idle

Think i have an exhaust leak in a 1999 s10 blazer lt 4x4 4 door. the loudest spot where i can hear the exhaust noise at cold start and idle, is the passenger side right behind the front tire. on cold mornings where you can see the exhaust smoke prior to warming up i cannot see anything coming from this area. non mechanic types have suggested either the y pipe, or where the y pipe meets the header. Would both have to be replaced to fix this problem if this is the case? and how intensive is this to fix? meaning would the whole motor have to be pulled to remove the entire exhaust piping to have it brazed? my dad is a mechanic, so the tools I've got and his know-how, just need to know what to do? Any definitive way to tell where an exhaust leak is, beyond having a friend cup their hand over the tail pipe, while they look for it..