Engine Noise

[Wildhorse]

98 MPV 4x4 loud pinging noise at start-up. Lasts until engine has warmed up then it is barely audible. Sounds like valves but not sure. Seems to be getting worse (louder and longer).

[gruss]

that would frighten me, if its pretty quiet and is just the valves, thats no biggie, try some lighter oil to get it up in the heads quicker. if its really loud and getting louder, perhaps turining into a clang clangy clang noise...ummm its gonna be ugly.
does it have a lot of miles or worked hard or anything? ever ran low on oil?
since it goes away my guess would be the valves though...a knocking rod typically doesnt "get better" when the engine is warm. if you cant tell where its coming from maybe find a stethoscope and listen around, try to pin point where the noise is coming from then work from there.