Upgrading from T1i to T4i?
The 18-135 is completely silent. Quality is excellent, I find a bit less chromatic aberration with 18-135 over the 18-55. In general T4i is a very nice camera - I have used and reviewed the crum out of it - lots of stuff here http://www.youtube.com/playlist?list=PLCUnGRSvb-aLtnE31FL9ROJgf1bxscQsN&feature=view_all
I am also happy to answer specific questions about it as it is in my hand this momentOne thing to note - you don't have to use the autofocus for all video and I cover that in my latest video http://www.youtube.com/watch?v=A8GtUN-b5y8
Hope that is helpful!