You were right haha. Put the car on the hoist this afternoon and starting grabbing and shaking things trying to replicate the noise. Managed to figure out if we pushed and pulled on the subframe it would consistently make the noise. Torqued all the subframe and diff bolts up, still no fix. So started torquing control arms bolts, no dice there either. Loosened one of the spherical bearings and it stopped making the noise, so we took the bolt out, pulled the bearing and removed the dust boot and whatnot.
Could actually shake the bearing inside the joint/race/outer bearing. It also didnt look like there was much grease in the joint which probably caused it to loosen up in the first place. We packed the joint with copper grease and put it back together and viola! No more knock.
I've since emailed USPmotorsports about this, so we will see what happens. I took a short video of the bearing making the sound to send them if need be. Fingers crossed they'll be happy to just send me another Spherical Bearing and I dont think it's hugely USP's fault as they get the bearings from FK spherical bearings in the US.
Also somehow I've been hit with bills amounting to the exact value of the next part of my wheel setup, and I need to do some maintenance on the car as well, so they'll have to be put on hold for now.
I'm planning on doing all fluids bar brake fluid because I'll do that in the coming months when I re-do all the brakes. Obviously I'm going to need Haldex fluid and filter, and rear diff fluid, but what have people used for their gearbox oil?
I was thinking a redline oil of some sort cus I know a lot of people use them. Just after some recommendations on what to use, my gearbox feels okay but would like to obviously prolong its life as much as possible haha.