First ill fill you in on what ive done in the last week with my truck:
1. installed k&n CAI
2. cleaned throttle body
3. a couple days ago i switched from 85 octane to 87 octane gas(i mixed the 2 cause i still had a 1/4 tank of 85)
4. I've been hearing a slight knock sound when turning and hitting a bump at the same time.

So...2 days ago i was driving and when i reached 50mph i let off the gas and coasted and heard a knocking sound, i could even feel the thumping through the gas pedal. The knocking gets more rapid the faster i go(not related to RPM's, related to MPH). I only notice it when im coasting above 30mph, i dont hear anything when im speeding up. There's no check engine light on. What could this be? Would bad ball joints or tie rod ends cause this noise? Or would mixing octanes cause it?

 

With my 5.9 octane don't really matter but I'm pretty sure the manual on the Hemi's says not to use any lower than 89 or something along those lines. Just a heads up, it can cause some serious motor issues running the lower octanes for long periods of time.

 

i dont think switching octane would cause that but the hemis call for 89 octane (i think)
i need to replace my ball joints but they dont make noise .

 

Yea sounds like those could be culprits. Possibly bad wheel bearing giving you a shutter. I'd say jack the truck up and check out your front suspension and yank on the wheels to see if there is any play. Also spin the wheel around and listen for anything odd.

Mixing octanes shouldn't affect it like that. Either way, hope it gets resolved. The unknowns are always the most aggravating.

 

sounds like a u-joint to me

 

and +1...you really shouldnt be driving a hemi with anything lower than 89. Running 85 in a hemi with a low altitude place like florida could really hurt that engine. Good thing you switched

 

i got the truck a few weeks ago and the guy who had it before me ran it on regular, my first 2 fill-ups i just stuck with the regular gas but decided to switch to mid grade after scanning through the manual and now shes doin this. I dont know if its the gas i used, or if its something else and the noise coincidentally started after filling up.

 

Ditto
Usually there is a squeak or chipping along with the vibration when coasting, but sort of goes away while under power.
good luck

 

I doubt the gas is what caused your problem and it's probably just coincidence that it started after your fill up. I wouldn't even run 87 in that thing if I were you. Start running at least 89 to ensure your Hemi lives a long happy life.

 

Thanks im definatley gonna check out the u joint then! Whats the best way to check it?