A300Man,
Someone more familiar with the 737-200 will be able to give you a better explanation than me, but I remember correctly 737-200s had(have) low bypass engines, ie small in diameter when viewed from the front. This means that more of the air drawn into the engine is routed through the core of the engine, where it is mixted with fuel and burnt, then chucked out the back at high speed. This makes these engines significantly louder than a modern turbo-fan engine which has a higher bypass ratio (= less air is fed through the core and accelerated and more is pushed outside the core by the fan(the big set of blades at the front of an engine on a more modern jet)) these means less noise as well due to the lower speed of the bypassed air. I suspect, but stand to be corrected, that when a -200 is put into reverse the cabin occupants hear a significant increase in noise due to more of the airflow being directed towards the cabin, as on a more modern jet, but it is relative - you start off with a noisier engine directing forward thrust parallel to the body and then direct it towards the body and you get a larger increase in cabin noise.
Hope that helps, and is indeed correct, having never flown one I feel a bit of a fraud!
PP