Noise is subjective. It's depends on what someone's point of reference is? The 2.5 is definitely much more noisy then a modern engine. Tractor like in my opinion. My other cars are much newer. I would give my 2.5 a 8-9.
I will say this though. Much of the noise is not the actual engine itself. My engine has 160K miles, uses no oil, has great compression. My old distributor made a knocking noise from a bad bushing. It sounded like a timing chain slap, mild engine knock or rocker noise. The knocking engine noise went way down when I replaced the distributor. It actually disappeared. After that I checked for noise with a engine stethoscope. The head and block sounded very smooth and quiet, no knocking or any weird noises anywhere. There was noise was from other accessories. The EGR pump clicks, the injectors tick, drive belt and pulleys make noise, fan whirl.