What could cause a subtle knocking noise in the engine when cold and only accelerating gets quicker faster you accelerate?

- Piston slap: Worn or damaged piston rings or skirts can create a knocking sound when the engine is cold. The noise may disappear or become less pronounced as the engine warms up and the metal expands.

- Timing chain or belt: A loose timing chain or belt can cause the camshaft and crankshaft to be misaligned, resulting in a knocking sound.

- Valve train components: Worn or damaged lifters, push rods, or rocker arms can also create a knocking noise.

- Rod bearing: A worn or damaged rod bearing can also cause a knocking noise.

- Main bearing: A worn or damaged main bearing can also cause a knocking noise.