Chevrolet Camaro 1967-2002 - Help Me!

I got my 99 Z28 this summer. Shortly after a brief honeymoon period of days on the highway I started noticing a problem. Over the past few weeks the preoblem has gotten significantly worse. Heres what's going on: When I start it up theres a metallic humming for a few seconds then it fades out not to be heard again. Only when I start it. Im not sure if thats related to my biggest quarrel: my 5.7 is wicked bogged down. I feel like im driving my old 92 corolla but the gas pedal doesnt want to go down. As soon as i let off the gas the car jerks and quickly decelerates also there is a loud "bonk" noise. As I continue on the preceeding problems worsen. The jerking happens when I brake and/or let off the gas and gets pretty noticable. The "bonk" noise also worsens into what sounds like a gun shooting through metal. Finally, the exhaust sound sounds less than impressive, its so quiet except for when it "bonks" or "bangs"! This is my dream car so i want it to be a head turner for the right reasons, any knowledgable/accurate advice will be greatly appreciated.

It could be anything, I would first start and put it on a tech 2. Go to a GM dealer and have them scan the computer. This is the first step and go from their.

Any idiot lights on? "Check engine" sounds like its not running on all cylinders? Is this a4 or m6? if its a4 it could be the trans or torque converter, but anyway I would take it to gm and get a full diagnostics test then post up on here for advice.

One more thing check all the fluids, how's the oil look and smell? What color is the trans fluid?

How much would this diagnostic check cost approx.? Its an a4 and when i accelerate it doesnt shift properly so it could very well be the trans. but i have no idea if thats the cause or an effect. Just had an oil change and the fluids were changed.