I've got a 2001 Diamante, 3.5L engine in the USA that has 178K on the clock. Sometimes when you turn the engine off, immediately there's a pretty loud and deep sound with noticeable vibration for about three seconds. It's like something had been running silently but then didn't like being shut off. The first time or two it did this, it scared the crap out of me as I'd never heard anything like that from a car. I remember the old domestic cars from the 1970s that might continue to run on for a few seconds due to carbon deposits in the heads but this is nothing like that. I can't tell from which part of the car the sound is coming from and you can actually feel it through the seats. Has anyone else experienced anything like this before? The car runs like a champ but when this occasionally happens, it will definitely get your attention. Comments and/or suggestions will be greatly appreciated.

 

'sound'...,
loud and deep. For three seconds.


Check for a midget in the boot with a double bass.

 

Akzle, that was not exactly the kind of info I was looking for.

 

youve provided about 30% of the information required to even begin guessing.

 

Akzle, can you tell me about what you need from the other 70% of info? Thanks.

 

Sounds like on the cooling fan motors is worn out. The one on the drivers side runs when the a/c is on and gets the most wear. Turn off the a/c compressor and shut the engine down and see if the noise disappears. If so, you need a new cooling fan.

 

Does it have a cold air intake? One thing you could try is open the hood with it running and have someone else shut the car off while you are looking at the engine, may be able to pinpoint where it's coming from.

 

"Sometimes
when you turn the engine off,
immediately there's a pretty
loud and deep sound with noticeable vibration"

this is all you said.


Rattle sound? Clunk? Squeal? Rubbing? Youve said 'not detonation', but i wouldnt rule it out yet.

Vibration in the seat? Wheel? Door? Floor? Whole car? Gear lever? Your hands?...

Specificity. 70% more of it.

At this stage im picking detonation with bad engine mount.

 

sorry, i see you did say 'feel through seats'
we still need to narrow down where it is coming from and what it sounds liek.