Yes this one does not use the upper spray arm and lower spray arm at the same time....that noise difference is the wash motor reversing and a ball inside the pump assembly moves and redirects that water into the upper arm.
Wire diagram and has info on what spray arm works and when.... link is here
...Acrobat reader required to view.
**The pump assembly is driven by a 1/12 HP,
shaded pole motor. Rotation is in the
counterclockwise direction at 3100 to 3200 RPM.
The motor drives a pump which supplies 100
percent filtered water at a rate to approximately
12 GPM to one spray arm at a time. The spray
arm's operation is alternated by small "pauses"
of the motor during the wash cycle.**
The ball inside the pump assembly should be checked to make sure it is not gooked up, upper arm and hose should be checked to make sure they are clear, wash motor may need ot be checked to make sure the impellor is not cracked or loose on the shaft, fills should be recheked.
Some other/more info is here
that may help as well.