Knocking sound coming from left (drive side) rear area

[JoeFromPA]

Completely missed tht you have a tiptronic - disregard my comment on shifting quality.

Here's the thing - a boxer six is inherently balanced but will still be rougher at lower speeds. Even with a broken engine mount, you should experience less vibration at medium high engine speeds - what you might get is harmonic resonance at certain speeds.

Anyway, I can't comment on the stuff behind your head, except to say that it's easy to access those things and check to see if they are on tight. IIRC, they are all tightened in back there by hand/latch. So if something is moving around, it probably became unlatched somehow. None of that shelf should move if it's latched properly, at least as it is on my car...

You can not truly inspect the engine mount until it's out of the car. Even from under the car, its true condition is hid behind some rubber buffers.

If your car's is the original, I'm betting 95% its shot. That being said, just because it's shot doesn't mean it's the cause of your clunk.

Other symptoms of a bad engine mount = feeling the engine move behind you (front to back & some twisting), watching tha tailpipe move a good amoutn when the car takes off pretty quickly from a full stop, and various vibrations and resonances.

It's basically a rubber ball around a metal support that holds your engine supported and stable, and the rubber rips and tears. I just started a thread this morning about my own recent replacement of the mount - you can see it in there and how ripped my 99 boxster's was.