Pull and Examine your Air Filter and look for ANY compromised Un-Metered Air getting into the Air Intake System. Check the Air Piping and Flex Hosing leading up to the Clamps holding the Tubing on the Throttle Body for any alterations that look "Non-OEM" and re-fit them to being
"STOCK-AS-A-CLOCK".
Any Modifications done outside of the OEM Design Intake Specs can often result in these weird events that happen only at certain RPM, Speeds, or Gearing...as in
"The Case of a Bone Dry Transfer Case" or even a Bone Dry Rear Differential involving what Nikola Tesla called
"The Power of Infinite Amplitude capable of destroying a New York High Rise Sky-Scraper Building....".
Take a Flashlight and examine the Transfer Case for any signs of Dirt collecting around "Wet" areas under there. If the Transfer Case is
WET...
it will prove to be almost Bone Dry Inside.
Here is a Video of this poorly designed Suspension Bridge
(absent the correct Fencing or Drape side draping properly installed along the horizontal plane of a bridge borders) that eventually ...Shook the "Galloping Gerty" Tacoma-Narrows Bridge to pieces while reacting to the Ever Increasing Vibration Amplitude it experienced in a 40 MPH Lateral Wind that got "In Tune" with its super-structure:
All Intake Manifold systems that employ Resonators ---
require --- that Special Device because the In-Coming inhalation of Air can
--- Bounce off of the Pistons and Valves on their Intake Strokes and set up Hyper-Sonic Rebounds --- that
MUST be absorbed, lest their "Harmonic Tune" level be reached and create Ungodly Noises when these high velocity sound waves cannot be dissipated from Internal Engine Components in the Rotating Assemblies.
The Two Part Harmonic Balancer bolted to the Crankshaft Nose is there for similar reasons...in order to absorb
---HORRENDOUS--- Longitudinal Vibrations that might destroy the Motor if allowed unlimited, Increasing Amplitude.
Unbalanced "Tire Hopping" is another example of hitting that precise Harmonic Sweet Spot that can make you wish your Mom never met your Dad... whenever on Long Drives while your Molars loosen up from experiencing this mostly preventable phenomena.
Once you hit that "Magic Sweet Spot" if these "Harmonics can get a "Toe-Hold" ...its Ever Increasing Amplitude can harm the engine internals and destroy the quality of the Driver's
"Inner Ear" comfort zone.
The same can be said for Modified or Gutted Cat Systems and the use of Un-Tuned Headers or "Home Made Exhaust Systems" where a lack of appreciation of the --
Real Problem Of Harmonics -- can eventually make driving
...One Total Misery.
PS... Watch Adam and Jamey on Myth-Busters showing
WHY Marching Army Troops only cross Bridges in a "Broken Step" Fashion... versus using the ordinary Military "Marching In Lock Step" Pattern.
Jamie Hyneman and Adam Savage find out if the rhythm of marching soldiers can collapse a bridge and if a rowing team is strong enough to pull Jamie up on water skis. They also investigate how much bacteria from the toilet settles on a toothbrush.
www.discovery.com