03 Impala - engine rattle

Have a 03 Impala with 150K miles. Getting a marble like rattle under the car when I hit the gas (not always, but 1/2 the time). Could this be the trans or the water pump? Its hard to locate the noise. It does not sound like its coming from the top of the motor.
Thanks:banghead:

My first guess might be that a torque converter bolt fell out.

Thanks much. I will look into that...

Thanks much. I will look into that...my car does the same thing,sounds like you don't have engine trouble if it's like mine it was the type of gas your using,try a different gas station and a highter grade of gas with highter octane in,see what happens

Thats pretty good advice. I've heard of 3.8s being picky about fuel. In the cases that I've seen though, the check engine light flashes while this "rattle" or spark knock occurs. Are you guys seeing check engine lights?

I don't get any engine lights when this happens, but I now just realized that it does seem to happen most often when the car has been running for over 30 minutes. When it does happens, I do believe that I sense a definite bog and I want to let off of the gas pedal so that it will stop. The rattle (like pennys being swirled around in a metal coffee can) normally only stops after I let the vehicle cool down. But again, its not a consistant noise. Very weird!

I don't get any engine lights when this happens, but I now just realized that it does seem to happen most often when the car has been running for over 30 minutes. When it does happens, I do believe that I sense a definite bog and I want to let off of the gas pedal so that it will stop. The rattle (like pennys being swirled around in a metal coffee can) normally only stops after I let the vehicle cool down. But again, its not a consistant noise. Very weird!use a different gas staion and a top grade fuel