HELP! 2009 Engine rattle(?) under medium-to-high stress(?)

Sounds like it might be chronic pre-ignition so you may want to check codes if you don't know what misfire feels and sounds like You may need to be told that it's happening by your car computer there are four codes for the 4 cylinders when they're misfiring sometimes it's very subtle and it's hard to detect sometimes people have no idea what misfiring is oh well just really doesn't matter We just need to find out if that's the case If so something probably needs to be cleaned plugs need to be changed possibly things like that The Prius is made for regular octane gasoline matter of fact I run sheets blue fuel in mine with no problems sometimes on an extreme hill or really trying to do stupid acceleration I can hear a trace of pre ignition but that's in most cars now The computers will allow that and then they start to make their adjustments so I think this is normal it's not excessively loud so I'm pretty sure this may not be happening to your car or it's happening way worse or you have a head gasket leak and you are literally slamming the springs in the torque plate which is possible usually your eyes are directed to the space in between the inverter in the back of the engine that's usually the torque plate springs Good luck

 

Based on the details you provided about your 2009 Toyota Prius with 223,000 miles, the loud, grinding noise you're experiencing at higher RPMs is likely due to an issue with one of the following components:
Worn or failing wheel bearings:
The high mileage on your Prius could have caused excessive wear on the wheel bearings. When under load at higher speeds, the failing bearings can produce a loud, grinding noise.
Worn driveline or differential:
The drivetrain components, such as the constant velocity (CV) joints, universal joints, or differential, may be worn out after so many miles. When under stress at higher RPMs, these parts can start making a grinding sound.
Problematic transmission:
If the noise is specifically happening when under acceleration, it could indicate an issue with the Prius' unique planetary-type continuously variable transmission (CVT). Worn CVT components can cause a grinding sound.
Failing engine bearings or bushings:
While less likely, the engine's internal bearings or rubber bushings that support the engine/transmission assembly may be worn, leading to the noise at higher revs.
The fact that the noise appears to be a one-time occurrence, rather than gradually increasing, suggests the problem may be intermittent. This could point to an electrical or sensor-related issue triggering the noise.
I would recommend having your local Toyota or ASE-certified mechanic inspect the vehicle as soon as possible to pinpoint the exact cause. Continuing to drive with this type of unusual noise could lead to further and more expensive damage. Let the mechanic diagnose the issue and provide recommendations for repair.

 

It kinda depends on what the rattle noise is. There's the rattle that results from an engine misfire (the damper disc between the engine and transmission is getting "slammed" back and forth).

There's the "something on the exhaust is vibrating against something else".

Then there's "something inside the engine has too much looseness" and is on it's way toward failure.

I might use a scantool to look at engine data from the ECM - specifically anything about misfires. When was the last time you replaced spark plugs or coils? (I only use NGK or Denso plugs, and Toyota- Denso coils. Only from a reputable source - not amazon or eBay - too many counterfeits).

Posted via the PriusChat mobile app.

 

Put the front end on jack stands with the wheels up in the air put the car in gear and don't accelerate like a moron just step on the gas lightly wheel spinning You have all that racket and noise going on now probably not your drive line You have no weight on it it's hanging in droop It's not loaded nothing really happening. If you have a bad wheel bearing and you take all the weight and whatnot off of it until you get it spinning really fast it should be pretty quiet so if you have all that racket with the front end off the ground and rolling you know say 10 or 20 mi an hour not 55. Then it's probably not in those systems heat shields and other kind of nonsense can get really loud on this car if allowed to get that loose If they are just pull them off with your hand and throw them in the trash they're completely unnecessary make no difference in any part of the vehicle at all except they're silver and they look good if they're in place and not rusted.

 

Oh yeah I'll have to remember that If you were to do that the clips on that thing would make a horrendous racket The clips on the air cleaner that flip down If they're not flipped up locked over the lid and slip down oh my God yeah I imagine that could scare somebody to death too funny.