I bought a 98 4runner a little over a month ago from up north, 170k miles seemed like a good deal with the condition and the price. I started noticing a thumping or knocking sound. I've heard a rod knock before and it really doesn't sound like one to me nor does it sound like a valve clearance issue, this is a low pitch noise that doesn't sound metal to metal. The sound does get faster with rpm and stays consistent with the rotation of the engine, but does not change in pitch and does not get any louder as rpm increases. It does seem to get louder as the engine warms up but only slightly. The oil level is correct and the oil is clean but I am going to change it in the next few days anyway. The noise sounds like it is coming from the drivers side and somewhere in the bottom end. It doesn't really seem to be effecting anything, it runs great, good power, and there isn't even a slight miss to the engine. Just wondering if it's any kind of a common problem. I know my pickup had a knock to it but it was just normal piston slap and never really effected how it ran. Right now the noise is more annoying then anything but has not gotten worse in the past month and i drive it a minimum of 350 miles a week. I am a mechanic and have been doing it a few years, i worked of a Toyota dealer for about 3 years but never really paid any attention to the 3.4 engine in the 4runner (never saw one with an internal issue though) and worked for a Chrysler dealer for 3 years so saw a lot of their junk. Now I'm a heavy equipment/diesel mechanic so everything i work on rattles, knocks, and is completely worn out, lol. I would appreciate anyone's opinion or experience on this issue. Thank you.