[rnln]

This is the second car I have knocking experience (2000 Lexus ES300). The car has been very nice, smooth and strong. It is still very smooth and strong but whenever we are going up the hill, it'll knock very bad/lound and weak. Off the hills to flat surface, it's back to normal. Multiple times, I did try to shift to 2nd and 1st but it's doesn't get better. Anyone know why/what?
Engine oil: valvoline 5/30
Thanks in advance.