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Was driving my Lunchbox last night and noticed noise coming from the gearbox .Not a grinding sound but growling , it happens in both forward and reverse . I thought it was just the tires on the floor but I picked it up and spun the rear wheels and the sound was still there the weird thing is when I spin the wheels and rotate the truck side to side the sound gets louder on the passenger side . Could this be a grease issue in the gear box ?

Could be a ball bearing failure...

Only one way to find out..take it apart and inspect. You could start by taking the motor off and checking the pinion & counter gear and see if there’s any debris floating around.

The bearings were new . Ya I suppose I will take apart was trying to avoid that but in I go.

as mentioned : only way to know for sure is to have a look inside. That said, a new bearing can fail (sometimes (sh) it happens, and generally would be even the most difficult to reach, just because otherwise there would be no fun )

Ya very true A sport tuned motor would not due any damage right ? Well in I go I will report back.

If you are using the original Tamiya pinion, replace it with a higher quality one. The original will wear quickly and can damage other gears and throw metal particles through the transmission.

Ok at the risk of sounding stupid what exactly am I looking for, all i see is looks like black grease not sure where it is from .Possible pinion rubbing somewhere but can't tell no wear marks , confused

Start with the pinion , has the set screw come loose ? its also possible with a very old Tamiya pinion that its simply worn out and its skipping on the spur gear , they are made of the softest aluminium in the world
next has it got bushings or bearings , if its got bearings check that they are all running smoothly , it really could be a bad bearing .

Ya still using original pinion it's all I had . Where do I find an upgrade ?

Ebay is easiest or if you have a local hobby shop , your looking for an 18 tooth 0.8 mod pinion , steel is best . you better count the teeth on it to be sure as I'm just guessing its the same as the Hornet .

Just looking to keep stockish one of the upgrades was the sport tuned motor, bearings (full) and a HD steering servo. Oh ya and Yeah racing oil filled dampers. How much grease do you need in the gear box any way.

Well did a total tear down to find out that for the most part everything looked good other than a heck of alot of grease in the diff spur gear the counter gear bevel gears every where gummed up good. So going to give her a really good clean and rebuild .

Do all the bearings spin freely?

Just to dog pile on, it would be good to get a steel pinion gear. Even brass is better than aluminum. It might not be your problem right now, but when worn the aluminum gear will damage the other gear it meshes with.

The gears just need enough lube to not be dry. Extra will usually get flung off.