If it’s not the engine itself then engine speed dependent noises tend to be torque converter or oil pump based if heard in Park & Neutral. Why it should make a noise specifically at 2000rpm and no other speed is much more difficult to fathom.

I believe you have a 4.8is with the 6HP26 transmission? I need to check because I don’t know if the pump flow control uses the same system as the 5-speed but one of the big challenges with the design of a fixed-displacement pump like the ones used in the 5HP24 (below) and 6HP26



is, once you’ve provided adequate flow at the minimum engine speed (say 600rpm), how do you then deal with the surplus flow when the pump is producing 10 times that amount of flow at 6000rpm – way in excess of what’s needed. In the 5HP24 there’s a flow control valve in the pump housing that deals with the excess flow by feeding it back into the suction side of the pump (thereby also saving power & reducing cavitation)



The flow control kicks in at 2000rpm (see graph) – you can see where I’m going here…



As I mentioned before, I need to check if the 6HP26 system is the same, but I was wondering if your noise might stem from the pump/flow-control area of the transmission?

On the 5HP24 the flow control valve can be removed and checked (spring free length should be 82mm)



by undoing the retaining plug on the LH side of the intermediate housing





I guess this isn't a particularly likely cause of your noise, but I will check to see if the 6-speed uses the same system.

Phil