XRAY - Model racing cars

I wish I had more time to race, might have figured this out by now. When I first start up my XT8 it sounds great, I pre-heat my motors with the competition heater, and runs like a champ, but about 5 min. into a race it gets this grinding noise, someone told me about it at the finals last Nov. and mentioned it sounded like a center diff. going bad, stripped it down and nothing looked bad. I talked with a couple of other Xray guys and they suggested it might be mesh in the diff housings, I think it was Brahnam ( i sure hope i spelled your name right) gave me a couple of the shims for the front and rear diff. noone ever made mention of the noise. Sure enough, the next race i attened in garland tx the noise was back, checked all gear meshes and stripped down the center diff. nothing appeared to be wrong. then it occured it might be my clutch bell shims, made no difference, when my truggy warms up, I mean like the diffs warm and the chassis warms up after racing. To make a long story longer, when i was tearing it down for the periodic cleaning, I noticed the gasket on the pipe/header was bad and leaking alot, just a nice lil hole facing the engine, could this be what is making what would sounds like a gear noise? I have yet to take it out on the track to test, but other than gear meshes, diff issues or clutch bell shimming; I can't think of anything else.

At one point I was having all sorts of weird drive train noises that I couldn't isolate. Oddly enough I decided to run a different motor one day and the noise went away. It was the motor making the noise the whole time.
There's nothing on the truck itself that should change from the time it's started until it's warm except for the engine. Try getting it warm where it makes the noise then kill it. Immediately roll the chassis by hand and see if you can hear or feel the noise. Then fire the motor back up and see if you can hear it.

I have tried changing the motor out, with one that I was doing the final break-in on, so I don't think its the motors, other than it might have been the Gasket, but not sure.

You hit the nail on the head Branham, it's more of a whining noise, it doesn't seem to be any louder the faster you go, the gears look great. I did notice when tearing it down, the disc wobbled a lit too much, could they make a bad noise if they moved around too much?