GenVibe - Community for Pontiac Vibe Enthusiasts

This an oddly specific question. 2009 Vibe GT. Does anyone know if the top passenger side motor mount is supposed to bulge at the bottom? I'm talking about the black steel part that mounts to the frame by the coolant tank-the cylinder with rubber in it-is there supposed to be a protrusion/bubble underneath it or does that mean the mount has failed?
Here's why I ask. I have significant vibration between 700 and 1100 RPM. Replacing that one mount (all others are new OEM) seems to eliminate or, at least reduce vibration, but only for a few hours. In that time, the engine gradually sinks lower on that side and the bubble on the bottom gets bigger, to a certain point, and then stays where it is and the vibration is back just as prior.
I figure:
A: the mount (replaced 3 times, OEM) keeps failing for some reason
B: the mount is fine and something else is causing vibration
Please let me know.
Thanks!

Have you replaced any other motor mounts? They typically should be replaced in pairs (sides together, front/back together).

I didn't do them in that order. I replaced rear/driver side, then front, then passenger side last. I still don't know if the passenger side mount is bad. Does it bulge at the bottom? The engine was rebuilt so there are a lot of potential errors that could cause this vibration that wasn't there before.

Not sure if any of this helps BUT here are pics of GOOD motor mounts and a couple pages out of the Vibe repair manual with some information!

Thanks! That looks just like mine. I guess it's not the mount(s). I'm leaning toward it being the balance shafts or some kind of rebuild error. It could be the exhaust since I had a new cat put on, but I doubt it. Any ideas are always appreciated. There may be something I haven't thought of that can cause vibration between 700 and 1100 RPM only.

I should add that, in addition to the vibration, the car jerks/shakes (sometimes hard) on start up.