Severe Knock/Rattle (maybe from transaxle?)

My wife called today on the side of the road with a strange knock/rattle sound from the front (engine/trans/etc) along with an apparent loss of power. (no prior warning signs -- just started) She wisely stopped driving, then called me, and we decided it would be wise to have it towed home.
(Let me take a moment to praise my wife who has always been extraordinarily attentive to the mechanical operation of her vehicles. I've always been the fleet mechanic, and if she has ever experienced anything out of the ordinary, she contacts me immediately. She's not frantic or unreasonable -- in fact she's fiercely independent -- she's simply a conscientious person, and I love that about her.)

So we get the car home and I begin looking into what's going on. Was hoping it would be something simple like a motor mount or exhaust shield... no such luck. Everything externally seems fine.

Video here taken from under the car:

Judging by the sound and the feel (by placing my hand) it seems the problem is in the transaxle.
Not sure where to go from here. Would really appreciate any input.

Thanks!

 

Hi all. Thanks for the quick responses.

Sorry... I should have included more of the vital stats.

143K miles. Oil level is perfect (just under the full mark)... exactly where it was when I changed it about 1K miles ago.

I've had this car for about 45K miles, about 14 months. It gets regular 10K mile oil changes with full synthetic. It only burns about a half a quart over 10K miles, so this engine is tight as a drum.

I don't have a service record from the previous owner, but I'm also not a newbie mechanic, and I've been all over/under this car -- it's in excellent condition. That's not to say that there can't be a serious problem with it... just that it's not some clapped out piece of junk on its last legs.

EDIT: Forgot to add: this knocking sound started without warning. She drove 150 miles on the highway, made two sales calls, and this started when she was on her way to her next account.

Again, thanks!

 

Funny you mention this. That video popped up when I posted mine on Youtube.

It does sound exactly like that. What's the theory on cause and effect? I can't in my mind figure out how faulty plugs could cause that knocking.

Plugs were changed at 100K miles with NGK iridium plugs. I bought them online, and they were among a long list of plugs that fit the Prius. They were not, however, the slightly more expensive plug recommended by folks on Prius Chat.

Was planning to buy some Denso SK16R11, or NGK IFR5A11 at the parts store today.

 

UPDATE: Just changed the spark plugs to NGK IFR5T11... no change.

And another set of symptoms I forgot to mention that may be quite important: She described a "bogging/lugging/lack of power" when this happened, and the car emits a strong sulfur odor while it's running.

 

Hadn't fueled up in a couple days, so bad gas seems unlikely. Have not cleaned the throttle body.

 

Excellent point! That would help isolate the noise. Will try that tomorrow morning.

 

Yes, the CEL is on.

i tried unhooking the #1 coil in an effort to diagnose the problem, that resulted in the "triangle of death".