Doctormarshal

I've just bought a 1996 Dual Cab Hilux. 2.8 litre straight (non-turbo) diesel. 220,000 kms. It's pretty tidy, but a few rattles. The problem is that the engine get's pretty noisy at freeway speeds. It generally revs at 3,000 revs doing 100 km/h. I've been driving turbo diesels for the last few years, but i would have thought it would e about 2,300 - 2,500 rpm. Anyone got any suggestions as to causes/solutions??