This is likely the ominous, "death rattle." Basically, on the passenger side, rear part of the motor, there is a timing chain. The guides on this are plastic. Over time the chain tensioner loses its tensioning force and the chain begins to slap into the plastic guide. That slapping is the noise you are likely hearing. Your mileage is about right. Experts recommend changing out the tensioner every 60k (be sure to properly prime that tensioner or or is useless). I changed my tensioner and there is a noticeable and significant decrease in the rattle sound. Fortunately, upon inspection my entire plastic guide snapped off from the block.. many of them begin to disinigrate into the oil because they are still attached to the block and the force of the chain slapping chips away at the plastic.
The major problem here, if this is your problem, is that the motor has to be pulled in order to access that timing chain. It can be done DIY if you are well-adept at mechanics. I will be doing mine here soon.
I hope this is not the case for you, but it is the first possibility you should eliminate, IMO.
EDIT: I'm swamped in time right now and the missus is nagging or I would post the good links on the issue, but all i can find right now is this:
The timing chain rattle is getting more noticeable on my 2001 Explorer 4x4 XLT V-6 4.0 SOHC. I've got 175K miles on it and would like to get another 2-3 years (approx 25K more miles) out of it (my daughter's college car). Is there any reason for me to consider a 'preventative repair' at an...
www.google.com
