[V8] Noise that is driving me absolutely CRAZY!!

[kyle leatherwood]

Ok everyone.  I have officially gotten tired of hearing this abnormal noise 
that my 91 V8 5 speed makes.  This noise ONLY appears when the engine gets 
to operating temperature. Between startup and operating temp, the engine is 
as quiet as a mouse (a tiny bit of lifter tick on occasion).  This noise 
sounds like there is a freaking diesel engine under the hood.  Engine has 
had entire t-belt service done with new bearings and rollers all around.  I 
have pulled both valve covers and checked cam chains, they are great.  I 
have pulled off the serp belt to eliminate accessory noise.  Odd thing is 
that Mark Willoughby's 4.2 5 speed makes the exact same noise.  Keith at 
Germanautoconnection says he rebuilt the entire valve train on a 4.2 once to 
try and eliminate the noise, but to no avail and told me not to worry about 
it.  Car drives beautifully, no loss of power of any kind.  AARRGG.

Anyway, as anal and picky as I am about my vehicles, this noise is driving 
me nuts, so I must find out what is causing it.  My 1990 with 130,000 miles 
makes no noise whatsoever, and this one only has 116,000 on it.

Has anyone out there run into this and found out what it is??

Any help with finding this out will save my sanity in driving this wonderful 
vehicle.

thanks,

Kyle