New to 996, Q2: Clunk under the rear seats

[Innov8]

My recent acquisition is a 2004 996 AE with 112k miles. I've been driving it for about 4 weeks and have replaced the engine mounts with Rennline Semi-solid mounts with yellow inserts (great product).

I knew the engine mounts were due as the tail pipe tips were sagging and you could hear and feel the movement in the rear. As with others, I have noticed more engine vibration with the new engine mounts and that the levels change with the ambient temperture and engine temp. The inserts soften slightly with the warmth.

I still get a dull clunk coming from (sounds like) below the rear seats... only where turning... hard right or left turn, even at low speeds produces a signal cluck about mid-turn. In a straight line, no particular sounds over bumps.

I checked the tranny mount with a floor jack and it moved only about 1/2 or 3/4" up before there seems to be more resistance on the floor jack...

Question: Is there something other than the front tranny mount that I should also consider? I need to lift the car onto jack stands and remove the belly pan to visually inspect the tranny mount. While I'm down there, would love to check/test other potential sources.

PS. When shifting... if I lift off the clucth slows, the engagement is smooth. If I lift off more spiritedly between 2-3, 3-4, 4-5, I get a thump as the clutch grabs. This is a completely different sound than above but maybe the relate?

Thx in advance for sharing your experience and knowledge.

[Innov8]

Update: The plastic ring around the air box snorkel has been isolated as the source of the clunking when turning right or left. I stuffed it with high-density foam pipe insulation. Temporary fix.

Question is, am I looking at a design/materials issue or is there something else going on that would cause the snorkel to flex where turning that would make that noise?

Any ideas on what to check next would be appreciated. Thank you.

[inaminit]

I had an intermittent clunk out of the same area-turned out that one of the feet that support the airbox was broken and loose-the whole airbox was moving. Check that out.