After having actual suspension clunks, due to a failed upper A arm bush, and loose sway bar center bushes, there was still a low speed 'clunking' over small road irregularities, but I could not sense at any other speed and it did not change with braking or cornering.
Finding suspension noises can be hard as it is normally such a tight set of bushes.
This noise sounded like a "knock" but was not very solid or metallic. It was similar to the noises I had got from the worn sway bar bushes.

After a few weeks analyzing, I found I could get a similar sound when hitting the bottom of the bumper. I could more reliably get a knocking sound when hitting the lower air dam plate under the bumper. I doubted that this set of plastic could make all the noise I heard inside but after pulling it off (8) , I found that the radiator air guide (8) was loose and is only clipped to the lower of the radiator and has or should have had some rubber isolators on 3 stand offs. The remains of the rubber isolators were there but it was equally evident that this was hitting and rubbing on the lower air plate.
What was not clear was what actually held this in place, it seems like nothing at the front and that these 3 standoffs just press on the bottom plate and hold it up. I did a drive with this all removed and had no knocking.

I added some single sided adhesive rubber to the item and ensured it was clipped back to the radiator and allowed the rubber to press on the lower plate and it has resolved the sounds I was hearing.

The offending item in the diagram is item 8 on the right that is help up by just resting on item 8 on the left.

It is strange now going over slight bump at slow speed and NOT getting any noises. Funny how you get used to a behavior.
175k miles now.

 

Thanks, found this post in the archives and having just reinstalled the lower radiator cowl but not yet reinstalled the under tray and having previously had a "rattle" that was not there this time on a short test drive, I'll be aware of the posibility when I replace the under tray. The odd thing was that the rattle usually appeared when the engine was still warming up and was under torque climbing a hill close to home and then would go away as the temps stabilized and driving on the level even if under the torque of acceleration. I also removed the air suspension compressor to replace the piston ring and it had been run up pretty high on the studs it hangs from so I left it lower thinking it might have caused the rattle by hitting the mount above it.

I did still have "knocks/clunks" from both sides going over rough patches at low speed that I have come to believe may be the Arnott front air shocks that were installed new when I bought the car 11 months and 7000 miles ago; although I have replaced the front stabelizer bar bushings, both engine mounts, and the transmission mount, those clunks have been there since purchase and still persist.

Thanks again for the advice on the #8 radiator cowl and under tray; there were no rubber isolators on the rectangular protusions on the bottom of my radiator cowl, but I'll try to add something to separate the two parts and try to get them better secured.

Two things I didn't see in the 2005 XJR parts diagram were the InterCooler coolant pump (the reason I had disassembled my SV8s front area) and the auxiliary coolant pump. Were these electric pumps not part of the XJR cooling system? Or just not shown in this diagram?

 

That tray does have clips on the back edge that when properly inserted into the support rail along the back edge of radiator hold quite firmly.

Here is a picture showing both auxiliary and intercooler pumps.

One thing I have just found quite disturbing is the fact that the norma connector that fits on the outlet flange of the coolant reservoir on my car leaks
if it is under even the slightest stress.

By that I mean if you press the norma connector on to the flange a little harder it will leak. If you lever the connector up or down a little it will leak.

This is using a brand new hose with the norma connector and with the clip locked in the correct position. The flange on my coolant tank is
absolutely fine along with the two opposed guides for the norma connector.

Normally there would not be any "deviation" from a comfortably aligned hose however with my slightly larger diameter pump I stressed the connection slightly so for now I have had to go back to my original aux pump.

 

Thanks, jackra_1,
I think I got my lower radiator cowl back in the clips OK and I added some wire ties to hold it up on the sides just in case, but I think what dsetter was saying is that his lower panel was contacting the protusions on the bottom of the lower cowl and making the clunk he heard.

Having burped my SC system and filled the reservoir to the max indicator with the bleed screw open, I drove my car a short distance, let it cool overnight, and the reservoir was down again by 20 ounces. I am thinking there is a leak somewhere even though I had done a pressure test at the reservior before and it did not leak down.

What is the norma connector? Is that the one on the bottom of the reservoir with a wire "keeper" that goes to the brown 3-way pipe above the auxiliary pump? I don't see any evidence of my "norma" connector leaking, but I do see how it could easily get some vertical tension on it from the other plumbing. Guess I need to put my car on ramps and just let it idle for a while and look for leaks, but it is too darn hot today to be out among the mosquitoes for very long.

 

Yes I see what Dsetter is saying.

Yes the Norma connecter is on a 3 way plastic "contortion". It connects to a hose that fits on the top of the pump and one Norma connector that fits horizontally onto that outlet circular flange on the bottom of the coolant reservoir.

I have spent two days chasing down coolant leaks after reinstalling my super charger!!!!!!

The first leak was that Norma connector and I thought that was the only but no it was not.

Coolant was leaking underneath the super charger and leaking down the back and down on top of the base of the EGR pipe.

To cut a very long story short which includes taking out the super charger again I found the leak.

It was a "self inflicted wound" and I dont know how I could make such a rookie mistake.

Where the thermostat housing "branch" attaches to the block on two sides, running over the sc pulley , there are two metal brackets, one on each side. a single screw thru the "branch" hold each bracket place. These brackets support wires on top.

Well the one on the left, looking at the engine, I had screwed in place on the inside of the branch against the engine block!!!

Just filling up the reservoir it would leak and run down the engine block to the rear. I could not see it from the front. However I could hear it very clearly when I blew into the coolant reservoir and at that stage could see some splashes of coolant right in front of my eyes.

I have run out of coolant so will not know until I get more tomorrow whether this is the end of the story.

I think that when I am hot and tired I should not work on my car!

 

I agree on the hot and tired part and I hate self inflicted wounds so I am inside today while it is 99 degrees outside. Hope you have found all the leaks (and I hope I find mine assuming there is one).