I've noticed my truck alot here lately under a light to moderate load has a rattling sound and it sounds most identical to valves rattling...its not quite intermittent...more common than not. any ideas?

 

When i put some sh1tty gas in my truck, sounds similar to what your talking about. Try different gas (??) maybe. How many miles you have on your truck? I now have 36K, and noticed it more than when it was newer, so i mostly stick to Shell OR 7-Eleven gas. Hope its nothing major!

 

I run BP and Exxon....truck has 9000 miles

 

Are your 4.6's the 2 valve/cyl or 3 valve/cyl? I have a 2002 F-150 with the 2 valve/cyl 4.6 and I recently started to notice a "spark knock" type of sound with light throttle especially if there was a strain on the engine such as going up a slight hill. The truck has 25,000+ miles on it. Most of the miles have been highway or secondary roads. Very little stop and go or local only driving. I use 87 octane gas, Shell as a matter of fact. Also I noticed at the same time I seem to have developed a minor exhaust leak. It's making the tell tale ticking sound upon acceleration.

Whimsey

 

all the 4.6 1/2 ton truck engines are still 2V engines....but that strain on the engine part is definately familiar....i may need to step up my octane

 

If a 4.6 is pinging/ knocking, I'd take a look at the mass air-flow sensor. Common for these to crap out, and a bad one will cause the motor to rattle like mad.

 

I have a Town Car with the 4.6 and 95,000 miles and it has done it since I have had it. It is sensative to humidity levels and elevation.