Knocking noise coming from the engine on 95 Buick Riviera 3.8 supercharged V6.

I have a 95 Buick Riviera with the 3.8 Supercharged V6. All of a sudden one day as I was
driving and the car suddenly began to make a loud knocking noise and has ever since!
Not only is it embarrassing but also puzzling as to what it is? Ive always done my own
repairs and Im sorta stumped here. There also is a heavy exhaust smell almost as if my
catalytic converter is also bad but these may be two separate issues. I have read about
the knocking noise possibly being the harmonic balancer. Is this correct and if so how do
I test that? Any and all suggestions would be VERY helpful. This car is my every day
driver and I need to repair this ASAP. Thanks