Recently my LS400 1996 had a major service for 200K (kms). The mechanic is not a LEXUS, but they service european cars. I have been with them since I've bought the car 2 years ago and I'm quite happy with the result.
This time, after major service, replacing timing belt, coolant, platinum spark plugs, auto transmission fluid, differential oil ..etc, I have 'noticeable' noise when I am accelerating (RPM shows 2). The noise will back to normal when it reaches the intended gear level. Before the service this car was dead quite. Eventhough I switch off my radio, I hardly hear any engine or transmission noise.
Now it has roaring noise, not loud, but sounds like a normal standard car. I don't expect this from my LS400.
I will return this car to my mechanic, but does anyone have any clue what might have gone wrong?? Thanks for any feedback.

Regards,
Josh