Thanks for the reply. I brought it back to the shop and the mechanic checked it. He said it's properly installed. I remember though that I was experiencing this shaking before. That is why I thought replacing the mounts will solve the problem. Then I was surprised last night when I saw the original mounts with 152k miles on it were still intact and no signs of cracking or leaking. Anyway, today I replaced all the spark plugs and the shaking is still present. The oils pressure gauge also bounces together with the shaking. It is funny because the shaking happens at Park or Neutral, not on gear which is common problem to older cars.