Do you have a ramped freewheel? (i.e., has the freewheel been replaced?) If inot, that's the way they all worked back in the day. If it all the teeth are identical and flat, no ramps, they are going to chatter in between gears. In the mid to late 80s, Shimano and Suntour came out with indexed shifting systems. At first they just tried angling the tips of the teeth to help facilitate shifting. It led to crisper shifting, but there was still a fair amount of noise in between gears. Then they came out with ramped gears that have shapes built into the gear profiles to give the shifting chain something to "grab onto" in between gears, producing nearly silent shifting.

The Cyclone is smooth-moving and gives nice shifts, but without a modern, ramped freewheel, there will always be chatter between gears.