So did the old shop vac in the tailpipe test the drivers & passenger side Y pipe connections are leaking.The driver side is almost 50% of the way around, and significant air the passenger side less so.

Using exhaust system paste externally to seal it up an see if the tick disappears or lessens as a start, it will need a proper repair.

This also likely explains the thud, I hit that area with a lot of wd40, which likely got into the system via the opening and ignited when the temp got hi enough which is why it never re-occurred, That would have also further damaged the y pipe gasket

 

Final update no more rapid tick, there is is still a tiny bit noise but it nothing like it was, I am taking this as win.

I did do a oil pressure test just in case as the paste needed the engine to run for 10 minutes to set up

Idle at 720 dropping to 660 once warm
52 psi at cold start
36 psi at 172F
30 psi at 183F to 186F
52 at 2000 rpm 181F
returning to 30 once rpm drops to idle

Note these are cold to warm numbers I need to to take the Disco for a run and expect a 10-15 psi drop