My 4023's Vanguard was fairly quiet at wot running the chipper. The chipper/t.pump was actually louder when up to speed than the tractors engine. Between the tractors pump, chipper motor, and chipper's inards spinning around, it was quite loud. Then add wood/brush and WOW, that was waaay loud. This is where it performed best and I always ran it wide open. Never had an issue at all. I did over load it once or twice and could hear the relief squeal, and waited a couple seconds for it to regain speed and kept on chippin'. It was by far the best attachment I had, well the most enjoyable.
The splitter was happy running just above idle. It would not split any better at full than 1/2 or what have you (setting) as it's a single stage pump directly off the tractor. Again, to me the most noise that comes from these (mine anyway) is the whine of the hydraulic pump. It did not bother me as it sounded like a serious piece of equipment, as it was.
I had a few pieces of miserable maple that got stuck as it is only rated at 9 tons. But went through all the red oak I had with ease. it was very quick too with a 10.7 second cycle time. I could split alot of wood in a short period of time all by myself. When my young son helped it was even faster.
The most impressive attachment (noise wise) was the deck. The rm48 was so smooth and quiet when running, the only noise was from the engine muffler. The hydra vac makes quite a bit of noise to.
I wore hearing protection at all time as I still do no matter what I'm running.