Engine vibration and loud noise at traffic jam and low speed.

How many miles?

 

Head gasket?

 

Vibrations can come from a lot of areas....be sure to check your engine mounts and get underneath and check all of the suspension, too, as well as tires.
My son-in-law had a horrible vibration in his 2008 Corolla and, after inspection, I discovered one of the front tires was WAY out of balance so we think one of the weights must've fallen off. Got it re-balanced and good as new!

 

Debatably not overdue for EGR cleaning. When you say “EGR pipe”, you mean just that short pipe between EGR valve and intake manifold? If so, I would not hesitate to clean the rest: the EGR valve/cooler assembly, and the intake manifold (has crucial EGR passages). More info in my signature.

I wouldn’t completely discount head gasket issue though: the carbon build in EGR is gradual, gradually compromising its function, not fine till 100k miles, then suddenly a problem.

I have to choose my words carefully: it’s my unproven suspicion carbon clogging of the EGR is a factor in head gasket failures.

You say it runs rough when hybrid battery state of charge hits minimum? How rough? Our 2010 seems to be a little noisier than usual when that happens.

 

Pinging because of low battery contribution and carbon buildup in the cylinders. Probably burns oil as well.

 

That's not good.

Something to keep in mind: carbon-clogging of the EGR circuit can lead to head gasket failure (unproven theory on my part). If you're having symptoms of head gasket failure, cleaning the EGR then will not reverse the head gasket failure.

Again, your miles are quite low still, but again, I don't see the EGR clogging, and it's effect on the head gasket, as happening overnight, at some particular mileage, say 100k. I'd say it happens gradually, and the point at which head gaskets fail can vary.

Boroscope inspection of the cylinder interiors with the coolant system pressurized (looking for coolant leaking into cylinder) is a good test. Also consider leak-down test, where air pressure is applied to the cylinders, one at a time when they're at top dead center of compression stroke, with a special set of gauges. Competent mechanics do both tests; they are a little tricky for DIY.

 

Unlike most of the people around here I have seen this before. It is pinging, otherwise known as preignition. In a conventional engine, it is carbon buildup in the cylinders leading to higher compression ratios. Combined with low octane gas that previously was fine, you get pinging. In a Prius the same factors are at work but the hybrid system depends highly on electric motor torque at low speeds for acceleration. So when the bars are very low and you have carbon in the cylinders, you get pinging. When the bars are higher, no pinging.

A new hybrid battery will solve it. High octane gas will probably reduce it or eliminate it. Cleaning the combustion chambers including the exposed valves and surfaces might help. I just replaced the weak hybrid battery and the behavior went away.

 

Carbon buildup, low octane, low battery. Pinging.

 

It might be good to run a bottle of Fuel Injector cleaner in the gas tank and give her an Italian Tuneup. Years ago, my mother-in-laws Avalon was only 3-4 years old but wasn't running very well, just didn't sound right. She let me borrow it and I got it up to operating temps, went on the highway, and floored it a few times. Ran MUCH better afterwards.