Ok, so at times, the engine vibration in my S can become quite signifigant. I mean, bad to the point of causing the top to rattle when it doesn't rattle normally. I have had a Honda dealer (one who I will never return to) look at this and the guy told me it was large amounts of exhaust gas causing the exhaust to vibrate the car. I was like but I had to go on vacation.

Anyway, anyone have any ideas? It seems to be worst under acceleration while in high gear. Predominately noticable at around 65 in 6th and accelerating.

 

Have you looked under the car? Check the motor mounts, check the mounts for the transmission, check the mounts for the diff.

Also, a speed-related vibration may be nothing more complicated than a wheel that is out of balance. Is the vibration related to the speed fr the car or the RPM of the engine? If it's the speed of the car, it's a wheel or suspension problem.

 

i kno exactly what you mean...
i get those vibrations too...

 

At 65 mph, in 6th gear, your engine is ticking at about 3500 rpm. I'm hypothesizing something but I would like to know if this vibration is still evident (and to the same extent) if you were to repeat this scenario but do it in 5th gear or even 4th gear. IE, get up to 65 mph in 5th (or 4th), then accelerate.
If it still vibrates the same, then you may have an issue with the CV joints, rear diff, or some suspension component. If it does not do it, then I'm suggesting that you might be trying to accelerate too rapidly from too low an rpm (engine lugging).

 

What mods do you have?

 

Ok, to answer questions in no order:
Motormounts-Good call, I will check the mounts I can see.
Lugging-This is an issue that has not always been, so I don't think it's my driving. I don't tend to downshift when lightly accelerating (This happens under cruise control as well) on the interstate.
Suspension- It's not a wheel or such. I've had an alignment and all 4 wheels have been balanced since this began.
Axle Halfshafts-Maybe, but Honda has worked on these 3 times now. Still clicking. I will be taking it back in for these....again.
Differential-Got a new diff early this year. It'd have to be a defective new.

And it happens more in an RPM range than speed. Also, it's less evident the lower the gear, but it definately varies compared to engine RPM.

 

If it's RPM related, then it's more likely engine in origin. I'm still going to say it has something related to lugging. I'm not saying that it's you, but rather, there might be something odd about your engine that is making it easier to lug under the conditions you stated.

On a side note:
What fluid did they put into your new diff? A new, good diff with the wrong fluid can easily turn into a bad, new diff.

 

Well, now, as with most Honda repairs so far, there's a funny story about the diff swap. It seems that this latest time I took the S to a different dealer since the previous one had had a less than sterling success rate of actually fixing the rear end clicking. The new dealer informed me that the previous dealer had failed to put the correct fluid in the differential when replacing it. They replaced the fluid then. Mebbe that's the issue.

 

It could be only one issue that might not be related to what's happening. A rear diff problem would not be rpm related, but rather, road speed related.

 

Could be why I still have the rear axle nut clicking noise. They say they have repaired it 3 times so far. Every time it comes back in less than a month.