New Omnibot Power Train

My Omnibot although brilliant is very noisy trundling about.

Also due to the original battery being a big heavy lump it now needs weighing down at the back to stop it lurching or rocking when starting up. Although the original motors are very capable/powerful to pull along all the weight I was wondering if anyone would recommend swapping to modified servo's are they going to be powerful enough and more importantly a lot less noisy?

Suggestions welcome