Insufficient information is given - but it could possibly be a sticking valve lifter that quiets down and the noise goes away after the engine is warm and the oil is circulating.
The fuel injectors make the ticking noise you hear at startup, especially when the engine is cold (colder temperatures).
Oil slow getting to the head
I think it needs a nose job, a.k.a., rhinoplasty.
It could be a sticking hydraulic lifter or valves that are slightly out of adjustment.
Could be a weak oil pump. The reason it is ticking is that the oil is not flowing to the lifters when it's cold. It's not that big of a deal.
I'm in the same boat: Try reading all pages on these links: http://townhall-talk.edmunds.com/direct/view/.f15850c/0 http://forums.automobilemag.com/70/6248778/toyota/2002-toyota-highlander-problems/index.html this one has photos how to do the repair: http://www.tundrasolutions.com/forums/highlander/32217-heater-quit-sort-of/
a "knocking" noise could be your lifters. and the ticking when accelerating and letting out of the gas is the same thing. check your oil and if it's full then you may need to think about either having them adjusted, or getting new ones. depending on what you have depends on whether or not you wanna sell it
It can depend on whether or not your area is subject to extreme heat or cold conditions but the usually recommended oil is SAE 10W-30.
Hereford or a Highlander
Could be your lifters hitting the inside of your valve covers, it may only do this when it is cold and when it warms it will stop. You could try loosening the bolts on your vavle cover
DOES IT HOLD GOOD OIL PRESSURE WHILE HOT AND IDLING? SOUNDS LIKE MAIN BEARINGS.
Lack of oil lubrication to lifters