Mystery Knock

Hey all, brand new to this forum and recently purchased a 08 Tundra with 93k miles. At the test drive the truck ran fine. A couple days later I noticed knock coming from the engine. It seems more notable when I put it in gear. There are times it is hardly noticeable. I did see the dealer did not replace the oil being the previous owner changed the oil about a month before he traded it in but the oil change was not done at a Toyota dealership. The car fax stated the previous owner was very diligent on maintenance and it was for part maintained by the Toyota dealer he purchased it from. I have read that these motors can be noisy,? Any thoughts on this??