Re: Loud grinding
The loud grinding noise when making a turn can be a CV joint from one of the axles.
Also if you have locking differentials, it could be a too low quantity of the limited slip additive.
The other knocking/grinding sound is coming from the engine? You mentioned you could hear it when idling. Have a look at the bearings from the accessory belt idler and tensioner pulleys. Those bearings get dry over time and start making noises. In worst case the bearing can even lock and the pulley will be destoyed, loosing the belt and all accessories. The worst one is the waterpump, because it can cause overheating when the engine is not shut down soon.