On this and one other model (a MG PRR C1 with a Faulhaber motor driving a NWSL Mod.6 gearbox) I've found the NWSL couplings to be quiet. With a tight clearance set on the adjustable rotation limiters I've not heard any chatter. That said I'll give the hose coupling approach a try on my next upgrade project. I do have some of that hose lying around. A couple of years ago the guy at our local Toyota parts department just gave me a foot of #0 hose when I told him I would be using it in a model train. 
In adition to the Sunset PRR J1 I also have a Westside one. It is slightly finer detailed than the Sunset but the Westside's drivers are undersized and like all KTM built PRR long distance tenders is several scale feet short. The Westside/KTM J1 exhibits some cogging running downgrade with a heavy train. To a lessor degree I also get some downgrade cogging with Westside M1's (same KTM gearbox). Jay - do you think installing ball bearings and thrust washers on the gearbox shaft would mittagate the cogging?
I didn't know about Matt's west coast connection.
