Left rear knocking noise 328.. after awesome track day.

Attended a SAFAC track day at Kylami raceway.
Drove behind awesome sounding yellow 348 up to the track. Really set the tone for the day.
My 328 with Tubi sounded as good i hope. You never can tell when you are driving, -- PITY--
My car was gleaming, looked -- NEW--. So did the 150 plus other cars there. I got out onto the track and raced it up against others of similar types and ate them up.
Pitted myself against 355's and 360's and had to smile when they overtook me easily even inside the racing line. Enzo, F40, F50 430 and CS'es all present and accounted for and plenty fast.
My vote for the best sounding car went to a 355 which simply screamed down the straights just like a F1. Dont bother talking when it passes. Its so loud and great sounding. It sounded much better than other 355's though. 360's sounded more rattly tinny. Two scuderia 360's based at the track were prolly as loud as the 355 mentioned but by no means as nice sounding.
I conclude nothing sounds like a 355 with exhaust. Unfortunately i have no idea which exhaust it had but its likely to have been a Tubi.

Now for the FUN part:

Driving home afterwards i turned right at slow speed and suddenly a loud "knock" "knock" "knock" in rhythm with the left passenger side rear wheel speed. Nothing to do with the engine as it persisted when i pressed the clutch and as the car coasted to a halt it slowed and quietened in synch with the wheel speed. Only a slow right turn generates this knocking from the left rear.

Looking at my GF in shock i noticed her roof latch was undone and a tentative bit of hope crept in. Perhaps the roof was bouncing and the latch was knocking as i turned right. Nothing doing though.. the knock persisted.

I listened at each right turn and it seemed to go away after some highway driving.
Next morning i tried to invoke the left rear noise again by driving a tight right slow circle and sure enough, but fainter than before, it was there.

Grasping the wheel and shaking it does not exhibit any wheel bearing play and there is nothing untoward looking about it. No grease, no dangly bits. No whining or grinding or chirping.

Crawling under the car best i could, i grasped the passenger side half shaft and shake it around. To MY amazement it moves. It slides left and right easily ie. along its length, about two inches in and out of the hub / diff. The boots look fine. Can't imagine its supposed to do this ?
Shaking it front to back it also exhibits limited movement and i can get it to make a faint cluck if i shake it vigorously enough.

The drivers side exhibits the exact same left right sliding movement but less front back / play and no amount of back / front shaking can get it to clunk.
I note on both sides that the forwards / backwards play is visually expressed in a tiny gaping or movement at the junction of shaft and hub. ( though this is all i can see with my head wedged firmly between the concrete and the suspension. ) The drivers side shaft is greasy but i conclude that my leaky cam seals are responsible for this.

I dont know how much of this deflection is normal.

Car is in superlative condition otherwise besides the drippy cam seals.( these leaks BTW started immediately after a cambelt replacement at 45000.00 km by dealer )
Its due for its 50 000 KM service now having rolled over to 50000 precisely at 240 km/h down the main straight this weekend. I would think this is a good omen

I do have aftermarket 18" wheels but only for the last 2000 km or so, which with Pirelli Rosso's gripped like hell in the corners, and its here that my counterparts felt my wrath on the track..

Otherwise i have had a totally problem free, besides standard aircon and Tacho problems ( untracked ) 15 000 km since i have owned this car over 10 years.

But what the hell do you think is knock knock knocking in the back there ?

Skin.