Unusual grinding noise when accelerating

As you continue to accelerate, does the noise stop at some point? Or, does the sound continue but perhaps you don't hear it due to road noise? If the AC is off, but the battery is still low, does it happen if you accelerate quickly, needing the engine right away? Can you localize the sound to one side or another, perhaps enlisting the help of a passenger to listen out the window?

 

It doesn't sound like an MG problem, seeing as it only happens at low SOC when the ICE is doing most of the work. If it was a transaxle problem you'd expect it to be just as noticeable at normal/high states of charge too.

So maybe it's something as simple as the heat shield on the exhaust rattling and rubbing. Or something similar that's happening when the ICE is under more strain and vibrates a bit more than usual. It might also be worth checking that all the engine mounts are good.

 

Bad wheel bearing. You definitely can get grinding noises, and sometimes clunking noises

 

Maybe bad ICE water pump? Check the pulley by hand for any motion while engine is off.

 

Trying to revive this old thread, I am having a very similar, if not the same, issue on my 2004. Car has 186k, work done has been usual timely oil changes, an HV battery swap with a rebuilt, 12v battery replacement, power steering system replacement due to a fight with a curb on ice, front strut/coil replacements with Detroit Axle easy swappers, NGK spark plugs, catalytic due to scumbag thieves, Millercat shield plate to protect cat and that is pretty much it. No dash lights, no codes, car behaves very well otherwise. My MPG seems to fluctuate as any in this year range, Spring/Fall averages about 45, Winter/Summer averages about 40. I believe it could use a look over on up-front bushings due to some bump bobble type noises but she drives straight and doesn't fight me in any way.

The noise on my vehicle only hits under certain conditions, too cold or too hot, there is a middle ground where it seems to go away...usually. The noise seems to come from the front right of the car (passenger) and mainly when the car is at a dead stop (ICE off and electric full stop) and you punch the accelerator. The noise almost sounds like a blend of heat shield rattle mixed with the noise of ABS activating, involving that slight grinding noise and sensation that accompanies ABS engagement. I can faintly feel a vibration accompany the noise/grind when it occurs. The wheels turn freely, no real hesitation and the noise/grind/rattle tapers off as the car gains speed. I can almost fully mitigate the noise from happening if I slowly bring the car up to speed from a dead stop rather than lay on the accelerator so it must be something that engages the driveline on takeoff and when it is put under instant heavy load? Occasionally the noise/grind will occur if I am at a low rolling speed, say to yield, and I punch the accelerator while the ICE and electric are already in low motion so that part baffles me as to why it seems to also sometimes happen when the car is fully fired-up so to speak. Could this be a bad water pump bearing that smooths out as the harmonics balance out? That is the only component I can think of in the general area of the engine bay where I suspect this noise/grind is coming from. I believe mine to be original to the car, shows no leaks and I have never run into an overheat warning due to poor performance.

I replaced my drive belt over the weekend, didn't seem to fix it. My pulley seems to be original to the car as well but shows no wobble or play. Did an oil change as well as transaxle change with Toyota ATF WS, no change in behavior. It baffles me. I don't believe there are any kind of clutch plates involved in this cars driveline are there? Like a glazed plate that is slipping on engagement or something?

I appreciate anyone that takes the time to read over this, you are not alone OP, my car has been driving me crazy for about 7-8 months with this seemingly same issue. The car is a tank, and this thing doesn't seem to bother it but I know something is wrong and I can't help but think it won't just resolve itself and get better, only get worse.

 

Same issue here! Just like VOXul describes it for his Prius.

Mine is a new-to-me 14 Prius C with 87k. Awful and hard to miss, split second intermittent grinding noise under mostly certain acceleration conditions. Usually when under the load of an incline or lost momentum but also under some ICE start-up conditions while parked but way more subdued. It's as if the synergy drive doesn't like a certain RPM range, a position on the eCVT or the way it engages ICE power from a stop or slow speeds.

Been a few weeks since I noticed this after having DIY installed a cat shield. Eventually I had a chance to take a look underneath again just to ensure everything looked OK and found no excessively loose heat shields or shrouds. Grinding noise is usually worse in the cold mornings but other than that car runs fine. If I modulate the accelerator gently or drive with maintaining forward momentum I can usually control the grinding noise from happening.

I will be taking it for an inspection at a Prius specialist shop next week in hopes he can diagnose it properly. I'll post a follow-up.