If you pop the hood and listen does it sound like it is at the top end of the engine?
If so, could be a dirty tappet, not working correctly (sealing when it should). Easiest way to try to fix this issue is:
Next oil change substitute one quart of marvel mystery oil, for a normal quart of oil you would normally put in (not add a quart, and be overfilled by a quart!). While you are driving, "marvel mystery oil", may clean it up, "marvel mystery oil" can be left in, until next change or you can run a new batch, read the bottle!
If you get it to quiet down, you might do what I do, I use oil stabilizer every oil change in my 1977 Jeep CJ 5. I drive it almost every day, and I rebuilt the engine in 1996, it is still going strong. (I did not use the stabilizer until my fourth oil change, I wanted to insure my cylinders were broke in well at about 12,000 miles)
I have not had to use it in my present CJ 5. I have had five other CJ 5's prior to this one, the marvel mystery oil, helped with several of them. I had one that would not stop, I used a little more drastic measure with it, by installing a push rod a few thousandths longer than the one that was pushing on the one that was doing the "tapping". That sorta just re-positioned the plunger inside the tappet and it began "sealing" as it should, and the tapping ceased.
It is also possible that the only way to fix this issue might be to replace the lifter (tappet), if this indeed is what is making your racket.
There are always "pros" and "cons" with everything. I am "pro" with trying the marvel mystery oil, it will not hurt nothing, but if you feel its a different issue other than just a rocker arm push rod tapping, you need to get other opinions.
Regardless how much time passes please return to this post (so we get a email notification) and let us know what is going on.
Images (Click to enlarge)
Sunday, May 20th, 2012 AT 4:09 AM