knocking noisr in the front part of the motor

hard to say but if it was in the timing cover area, the noise would not go away. sounds internal from your description. take it to a shop and have them evaluate it and give you a bid. engine work is very expensive and whatever bid you get will only be the start till they open it up and see what the failure is. roy

Your RAV4 has a timing belt, so I doubt it is the belt. As the previous respondent stated, it could be one of many things: belt tensioner, internal mechanical problem, water pump, etc. I would suggest you have someone look into it before it escalates into a more expensive problem.