[GTP Dad]

Actually this sounds like the catalytic convertor is causing you problems. The loss of power may be due to it being blocked or partially blocked. The putt putt you hear may be due to the back pressure from the blocked cat. Try removing it or unhooking it from the exhaust to see what happens. If you have leaking intake gaskets and water is being introduced into the exhaust this can cause the cat to go bad. Good Luck!