Hello, My Monte Carlo with a.

Hello,

My Monte Carlo with a 3800 Series II engine has recently started making a loud exhaust-leak type noise in the engine compartment. It must be close to the firewall because you can hear while driving really well. I took it to an exhaust shop and they did a check on the exhaust sysyem and they could not find a leak anywhere. It's louder the colder it gets and when it's under a load going up an incline. I haven't had any DTCs since it has been doing it so I take it it's not electrical. The exhaust shop told me not to worry much about it but I know something is wrong and would like to know if anyone could give me some pointers of what would be causing this kind of noise.

Thank you in advance for the help,

Nathaniel