Keep in mind that the BFG AT's you are running are not the quietest tyre on the bitumen. If the sound is changing as the bitumen surface changes this indicated that the noise is starting at the tyres and travelling upwards. However as you have stated any rubber bushes that are pretty much gone and are possibly metal near metal will make the noise amplify ten fold.

If the noise is still somewhat evident after your susp work I would borrow some road tyres from someone and give that a go.

I replaced BFG A/Ts with pirelli A/T a while ago and way quieter. Not s##t canning BFG either, great tyres just a bit noisy.

Cheers, Dave