With less than 25K miles, we hear (and sometimes feel vibrations) intermittent popping sounds; like popcorn. Sometimes muffled, sometimes pretty loud. Otherwise, no problem mechanically that I can tell. When I attempt to rev it up, it sputters at 3,500 rpm. A friend suggests it may be the catalytic converter. Baffled.
Your friend may mean that he/she suspects unburned fuel is igniting in the converter. Sputtering may be too much fuel being introduced, hence the suspicion.
You should be lighting up the Check Engine Light. Are you? There should be fault codes in the computer that can provide a good starting point.
Given the age of the car, when was the last “tune-up”. Even if there are no codes stored I will still take a look at the spark plugs and consider changing them along with the wires.