Engine Vibration When Wet?

[johncc]

Hi all-

I've noticed my car is really noisy in the wet. There's a lot of rumbling and noise from the front wheels. However there is one noise that I think is engine related and not wheel related. It seems to occur at a particular RPM in several gears and stops if I let the clutch out. It seems to happens when the NS wheels run through puddles and it lasts for a few seconds after you get out of the puddles. It is a noisy vibration that you can feel through the steering.

Any clues as to what I should look for?

Thanks

[Derek]

I suspect that it may be related to the tyres.

[johncc]

That's what I thought, and at least some of the extra noise may be. But this serious vibration is definitely RPM dependant, not speed dependant. If you let the clutch out (and the revs fall) it goes away. Revving through the range while freewheeling with the clutch out, you hear/feel it at the 2-2.5K RPM area.

[sgould]

The tyres on my 9-5 (Michelin Primacy) are very noisy in the wet on certain surfaces or in water depths. I get the feeling they resonate and the noise builds up rather than just producing a noise suddenly, if you know what I mean.

As to your other vibration I had a similar problem (not Saab) which turned out to be a partial crack in the exhaust flex section which allowed the pipe to wobble in all the places it wasn't designed to do.

[johncc]

Speculating wildly, I think there is a misfire in this rev range already. Normally it is only present as a hesitation. In damp or wet weather, it is audible as slightly increased noise. After the NS going through a puddle it becomes very pronounced. Possible? I wonder if it is to do with the effect of water on the DI, given that hesitation in this range is DI symptom, and given that the intake is down in the NS wing? Also given that, although I have a receipt for a new DI about 2 or 3 years ago, when I changed the plugs for NGK's there were Bosch ones fitted. I wonder...