Hi Terri,
We initially booked an H cabin on the Voyager for our Baltics cruise this August. Upon giving it more thought and after weighing some people's less than favorable experiences in H cabin locations, we opted to change to a G cabin. Our reasoning was why chance having any difficulties with vibration, if, indeed, there were any vibrations to be felt? We just didn't want to risk it.
In my opinion, the cost is negligible, when you wish to ensure as smoothe a sailing as possible.
We sailed on the Voyager (G cabin) in 2003. It's a beautiful ship. I hope you are able to sail on the Voyager, as well!