1998 Weird Noise

Okay help me out. My tacoma is 4x4 2.7 4cyl just hit 140K miles. I bought it about 3 month ago and it didnt really have any previous service history. So far it's ran great untill the noise it made today! Upon start up she made a loud grinding noise and continued as i drove down the road at least 10 minutes prob. until warmed up. Reminded me of the noise a water pump makes when the bearing takes a crap. I inspected the water pump and fan and didn't notice any leaking fluid or unusual play in the fan.... Could it be my timing chain guide. Everything ive searched says these motors are suppose to be bullet proof and not require a timing chain replacement untill 200k. Is there anything else I'm over looking? Please help! Thanks