Why does my 2002 Chevy Suburban sound like a diesel?

Just bought my 2002 suburban. Oil was old and low so I just changed it. It has 70,000 miles and I put a high mileage synthetic blend in it. When you start it up it sounds like a diesel. Only for the first couple minutes of driving then it quiets down.

Any ideas?

Sounds like bad bearings in the engine. The previous owner had put heavy weight oil in it to hide the problem...