95 2.3L problems

I just bought a 95 grand am it it seems to have a slight knock or somthing, It sounds like a lifter at an idol but as you rev it slightly it goes away and comes back a little louder and more "tinny" at a higher rpm. It drives down the road fine and you cant hear it knocking or ticking in the car, It is funny that way. I would think if it were a knock it would get louder at a rev and be very noticeable at 70mph. This one you can only really hear at an idol or drivin slowly like in a parking lot. The car has 108K and the temp is great. It dosent have an oil preasure gauge but the temp stays good so i assume it getting the correct oil requirement.?? I drove it on a 2hr road trip today and it got 34 mpg. WHAT COULD BE WRONG? does it sound like a knock or is a problem elsewhere? Please help
Thanks

Could be your timing chain slapping on the guides. Any idea on how often the oil was changed?

I have no idea when the oil was changed. if i had to guess it wasnt often enough because the interior was trashed like a family of smoking pigs lived in it and didnt care. The oil is clean now and dosent smell bad. I just bought the car, the body is perfect and i figured if i parted it i could break even, maybe? I thought it was the timeing chain tensioner at first but the noise seems to be comming from the drives side of the motor. i will try to get a viedo clip of the motor running with sound.