Welcome to AF!!
I really can't tell based on your description what may be going on with your car. Can you better isolate where the noise is coming from? If it is coming from the engine it could be a rod or piston slap. If it is coming from the front of the engine it could be the harmonic balancer, timing chain, serpentine belt components or water pump. If it is coming from the area around the transmission housing it could be the flywheel, axle shaft or if automatic the torque convertor. Try to isolate the noise and post again.