Thanks for the fast reply Jake.
I'll try to remove the amplifier to see whether that helps. The antenna is located on the roof outside pointing toward DT Seattle where majority of the big 3 channels located (ABC, NBC, CBS). I tried to point to between the tree across the freeway but it's hard. Especially when the wind is blowing. Connection is especially good when I'm touching the antenna but as soon as I'm down from the roof, the reception started to degrade again. :-(
So will replacing antenna to a better one solve the problem or it's not going to make any different because of the trees? Please advise?