So just got an oil change on my 2005 jeep liberty 3.7, all of a sudden i hear a knock from the engine area. It is like every 5 seconds or so I hear this knock (only can hear if by a building or with hood up) and it sounds like the engine is losing power, almost like when the fan kicks on but this happens over and over...1 knock it SEEMS like its losing power (quiets down) then 5 seconds later another knock then it goes back to normal and does this over and over. Does not get worse while driving around, Any ideas? Ill be taking it in first thing in the morning.