Product review (5 stars): Great Solution to a Noisy Dishwasher
I ordered this part for my GE dishwasher after it developed a rattling vibration over a few years of use.  Additionally, when the loud vibration noise would occur, the dishwasher would not clean the dishes well at all - detergent was left dripping down the door where the detergent hatch had opened, the dishes wouldn't be cleaned sufficiently.

When I first started troubleshooting the problem, I replaced the sprayer arm, the circulation pump, and a few other components without completely fixing the problem.  I also cleaned out the dishwasher completely.  Residue had built up over the years in the sump, the sprayer arms, and the pumps (main circulation pump and drain pump).  In some online forums posts, someone suggested replacing this part to solve the vibration / noise problem.  There is a hub on this part which sits in the bottom of your dishwaher, directly above the main pump.  The bottom sprayer arm sits in this hub and rotates around with the water pressure.  The only thing I can think of is that the hub might have been worn just enough that the arm rotating in the hub had enough play that it would vibrate, preventing it from rotating freely.  Although I inspected the old hub didn't see any problems at all, the new part solved the problem 100% and prevented me from throwing this dishwasher through a window and buying a new one.

Couple more suggestions - I'm guessing that the build up of detergent residue and gunk led to this problem.  I came across several ideas from other people.  Once a month, run your dishwasher through a cycle with just a cup of vinegar in it.  This will help cut through the detergent scum.  Secondly, use a good detergent.  The two that were suggested are Cascade Complete and Finish Quantum.  I've tried both of them and they work fine.  Of course, now that the dishwasher is working well, I'm sure the cheap junk I was using from Walmart would work as well.  The key is that I don't want the detergent residue to cause problems again.

I'm semi mechanically inclined, and I didn't find replacing this part too difficult.  Of course, through the saga of fixing the dishwasher, I got pretty good at pulling it out from under the counter, flipping it over without dumping water all over the kitchen, disassembling it and putting it back together.  I'm pretty sure that you can replace this particular part without removing the dishwasher from underneath the counter.  I removed the upper rack to replace this part and, in the process, broke the plastic stops that keep the upper rack in the track.  So, I bought a few extras at some online part store for a couple dollars each.  I think you could get this in without removing the upper rack.