The Theta 2 engine fiited in Sonata YF is famous for it "harsh" noise, then again a "noisier" owner wouldn't bother.
Use to drove a 3rd & 4th generation Sonata, same thing "noisy" during harsh acceleration, seem like not much improvement after all this year.
jolokia,
If you haven't tried the Forte 2.0, Koup 2.0, Sonata 2.0 NF, Rondo 2.0, I suggest you do so now. That is how quiet the engine sound is when not tuned to way above 160ps. It is clear that you are lying if you said you did as these cars have silent engine and do not choke like Lavina/X-Gear when shifting gears.
The new Sonata YF 2.0L if you want it to have silent engine, you could always detune to 156ps@6200rpm with pulling power still remarkable at 194Nm@4300rpm. It still beat the Sylphy and Teana anytime in performance, handling, NVH, FC, maintenance cost, reliability, durability and practicality. Even resale value since you plan to degrade the Sylphy to B-segment in terms of price and class whereas Teana, it is already a proven failure that even China is phasing it off soon. The new replacement is Altima 2013, not Teana. Cars with short sales lifespan and not available in many countries will usually depreciate badly especially exterior and interior parts manufactured will be less. US and EU don't even have Teana.
If you bought a Sonata or Optima, these 2 cars are available globally and many users. Spare parts are widely manufactured and since the sales here is healthy with more than minimum required number of owners, spare part shops automatically imported bulk spare parts. If SC lousy also, there are many parts and proper workshops especially sub-franchised ones could get things fixed for you. RV for these 2 sure good if these requirements are met.