Are you feeling it only or are you hearing it also? I had a vibration I could feel and a knocking noise taking off and any time I got on the gas, worse on a down shift. I replaced both lower motor mounts the problem went away. You can get stock mounts from Ford or there are a couple of guys on here that take mounts and make them solid. I'm using SVT spec. mounts for what its worth. I've noticed less wheelhop but more vibration. I'm also using the the solid inserts on the front mount.
I replaced both my mounts in about an hour and I think the cost was about $140.
