problemwith my ls

[ursojp]

if anyone knows what the problem might be, can you please help me out. i have an 03 ls v8 with only 38 thousand miles. when im driving, if i push on the gas and it drops to a lower gear the engine sounds like a rattling machine. almost like an old chevy diesel engine noise. also on a cold start up, the car shakes and it sounds like 1 or 2 cylinders arent firing. almost like i have a performance camshaft. does anyone know what the problem might be?

 

[Amoxi]

Take it to the dealership. It's still under waranty, right?

 

[ursojp]

yeah i just wanted to get an idea of what might be wrong

 

[decibels5]

kind of sounds like bad gas, is it a solid,like metal to metal rattling, or kind of like valves chattering. all lss chatter with bad, cheap, or low octane gas.