My 97 3.4 has a slight ticking noise at low RPM when warm. It goes away at about 1000rpm but doesn't seem to directly corelate to rpm. I can't hear it from under the hood, just while driving. 4Runner has just over 200000 on it. Still doesn't use any oil and I would like to keep it around for many more years. Anybody have any ideas what could cause this noise?