2003 Honda Accord Clunk sound on light acceleration

Whether in park, drive or brake torquing, when I press the gas pedal slightly, I hear a brief clunk. Sounds just like one heartbeat, thump, bump sound. Had a friend listen while the engine was running and the hood up but could not locate it. There is a slight click coming from what appears to be an emissions type component of the very top of the engine but the thump is somewhere else. Again, I have to press the gas slightly to hear it.

Thanks in advance for an help.