Sounds like a bad CV Joint / Axel shaft. I would check the left wheel bearing and brake components first.
It is most likely a straight 6
open up your hood and look straight ahead and you will see it.
Wheel bearing
When you drive over a clicking bettle.
A loud clicking sound coming from the front of your car when you are driving straight would be the result of a bad CV joint. This is something that should be checked out right away.
Bonded Grinding Wheels for Metals are available in Straight Wheels, Cup Type, Discs Type, Soser Type, Large Inside Dia Specific Type etc.
Straight from the service manuals:2000 Silverado 2500 6.0 spark plug gap should be:1.524 mm (0.060 in).
Power Steering Pump
On the turn signal switch, click it towards you or straight back.The headlights are dimmed by clicking the turn signal lever toward you or straight back.
i don't think u really need cats because i have an 04 2500hd diesel silverado an i have stack pipes with no muffler no cats all straight pipes an is not loud but i don't know about gas if urs is
your front cv boot is tore. Replace this.
A bad wheel bearing also when turning it sounds worst or straight driving