You never really know what viscosity was in the engine when you got it, could it be a higher viscosity masking a problem? possibly, you never know. If it were me, I would change the oil and filter, maybe a good 5w40 - 10w40, give it a run of about 2k and then change it again. If it were flakes from work done then you will not see nearly as much this time. The change you do would be the sample to send in because you know what you poured in and the true run time on the oil. After this you can begin diagnosing.