2003 XJ8 VDP

I noticed this when I was stuck in stop and go traffic. When I apply the gas lightly from rest there is a light "thump" that I hear from the rear. I can feel this "thump" as well. When I let off the gas at low speeds (<10 MPH) I hear/feel it again. It is very subtle and I only noticed because radio was off and windows were open with no fans going. Any thoughts?

 

Who is in the trunk? Sorry, couldn't resist. You might try the simplest first and see if anything like the battery holdown came loose.

 

Haha I do have a bunch of crap in the trunk. That was the first thing I checked though. I should mention, this only happens when its warmed up.

 

I have had this in my previous rear wheel drive car, probably the rear differential

I brushed it off, until my differential crapped out on me, not a noise you want to hear traveling at 90 mph. When I pulled it apart I was surprised the wheels didn't lock up or the case explode, it was a total mess inside.

ALSO,

Since the differential is not directly bolt to the main frame, check the subframe mounts.