Things that would make a loud rattle underneath on acceleration at low speeds

[JCruse]

I'm getting a loud metallic rattle from underneath at certain RPM's while accelerating at low speeds. Especially under load like turning a corner from stopped or getting going in deep sand, but now it's beginning to happen while going straight. It's really loud too and turns heads.
I saw what looks like a heavy plate under the tranny or transfer case and that's the general area it's coming from. What could cause such a racket?

 

[harrydunn]

May be your cat shields or your trans skid guard. My cat shields rattle.

 

[LC8pilot]

Mine had a rattle like you describe. My O2 sensors had both come loose (from the bungs being so corroded) that they started to rattle like mad. I didn't notice it at first because they looked fine when glancing at them - only discovered it once I wiggled one & it came free in my hand.

Worth a check.

 

[Chaldaean]

Worn U-Joints can be pretty loud.

 

[bigfj62]

i just fixed that same rattle today. My heat shields on the down pipe just before the cat rusted loose. I wrapped a piece of wire around it and twisted it tight. Quick fix and cheap but the best part is no more rattle.

 

[coax]

My incredibly loud rattle was the front and middle rubber exhaust mounts/bushings had failed, and let the up-and-over exhaust pipe hit the rear crossmember due to decreased clearance. Its a quick 30 second check, so well worth it.

I ended up getting replacements off Amazon since it was small parts w/ free shipping.

http://www.amazon.com/Bosal-255-726-Exhaust-System-Hanger/dp/B00180J90I

 

[94SRUNNER]

I had a timing issue (advanced a number of degrees) last year that was causing a very bad engine ping, which sounds like a bad heat shield rattle. It occurred almost always under load at slower speeds. We set the engine timing to the factory recommended timing (3*) and the rattle was gone. It is a low (maybe zero) cost recommendation.

 

[ToyotaDon]

Best case scenario, it's a heat shield or skid plate loose or contacting moving parts. Worst case I can think of is a broken flexplate.

 

[thatcabledude]

My incredibly loud rattle was the front and middle rubber exhaust mounts/bushings had failed, and let the up-and-over exhaust pipe hit the rear crossmember due to decreased clearance. Its a quick 30 second check, so well worth it.

x2 Same thing happened to me.

OP, does your truck have sliders? My exhaust was also rattling on my slider when the hangers failed.

 

[Funner]

Recent wedding and you still have cans dragging behind, or worse yet, one is tangled up under the truck?































Or what they said- Heat shield etc. I doubt pre-detonation could get loud enough to cause head turning.