Exhaust leak noise when first started

I have a 14 model qx80 and when I first start it it sounds like an exhaust leak on passenger side for about 15-20 seconds then goes away and sound normal. I bout an exhaust manifold with cat hoping that’s the issue’s ,has anyone else have this issue. Dealer states 2500 to change it. Someone said maybe a timing chain issue? I’m not to familiar with Infinity/Nissan brands.