The Monterosport should NOT even be here in this comparo!
The powerplant in that thing is just a PRETENDER - lumang makina (1990's pa) na sinalpakan lang ng VGT na INIWAGAYWAY na ng Mitsubushi sa madlang people na animo'y kala mo sila nag-imbento ng Variable Geometry Turbocharger bwahehe.... Abah, abah, ang dami naman naniwalang Juan dela Cruz hehe....
I think you're right,my brother-in-law's monty is smoke belch car and ang ingay pa ng makina nya unlike sa fortuner na quiet lang.
The smoke belching issue is relating to how the driver uses the vehicle. If your routine is reving it hard all the time, then you will really emit dark grey/black soot/smoke. Try just running it/coasting it around 1500-2000rpm and not revving it hard beyond 2000rpm when you really don't need to, you will see a difference, both in fuel economy and the "belching" problem.
Also, about the noise, both the Fortuner and Montero are noisy. It just so happens that when the Montero is run from a cold-start (meaning its engine temp is cold from the get go), the engine is much noisier. Try turning it off mid trip and turning it on again, the noise level is different and the response is as well.
If you want a quiet diesel, the Koreans have the engine. Their is more "refined" in that regard of engine "noise" levels. The americans, in general, have better sound insulation but it weighs the vehicle down a bit. This is against counterparts of other brands available locally.
So basically "pick your poison" as they say.
Oh, and as a fellow Monty owner, if it is too noisy, maybe he misses his PMS or takes too long to have his serviced. every 5k kms, 15k kms, etc etc, you need to top up. Also, during every interval of 20k which counts as heavy, you are given a fuel line cleaner which you should feed into the fuel tank when it contains 40L or more FYI.