Q: Noise under the hood when idling and 1st gear.

Sounded like slowing till almost stopped and would struggle to get going again. Came from engine and is a familiar sound but it's like was beating out of time and slowing down. Started w/in 5 minutes of driving (third time that day). Lasted 10 min. Turned car off. Believe turned it on and still heard it then was left off 15 min and gone when turned on again. No warning lights, check engine, overheating. Told head and radiator no good after bought. sometimes lurches when accelerate like pushing & releasing pedal abruptly. Found out after purchased there's a problem causing the passenger's carpet (evaporator or heater core?) to be wet and was oil in water reservoir, but problem appears gone after radiator flush. Someone said clogged catalytic converter Someone else said air filter clogged due to strong winds day before. I've replaced spark plugs, brakes, and battery. Radiator flush 6 mo ago. 2 door int. handles have broken within really short time. AWD 16.5mpg

My car has 98000 miles.
My car has an automatic transmission.