Correct. My bike has a stock exhaust and sounds like a sewing machine, but I wear earplugs mostly to protect against the constant wind noise at speed.
Obviously higher speeds=higher wind noise; you might be fine < 35mph (~ 55kmh) in a city, but anything above that hearing protection is advisable.
"Measurements of motorcycle riding noise levels vary, but are generally around 85-95 dB at speeds up to 35 mph, climbing to 110-116 dB at 65 mph"