Hi guys,

So I have noticed this since I bought the car, but haven't thought too much of it (and have been spending time 'debugging' the symptoms, so to speak).

In a nutshell, when I am at speed (typically over 90 or 100 km/h (over 55 mph)) I notice a sort of low-pitched harmonic vibration (which I can both hear and feel). I can't really localize where I feel it - I can feel it through my seat (though it's not a strong vibration) and through the armrest. Not through the gearshift at all. The vibration is not constant - it's more of a vibration that gets weak, and then strong over the course of about a second or a little longer.

If I shift into N while driving, and take my foot of the go pedal, the vibration is totally unchanged. I imagine that if I were really interested, I could shift into N, take my foot off and then even go so far as to turn off the motor and it would still be the same vibration.

If I let off the gas (while still in D, at speed) the vibration becomes a little stronger (but only slightly).

Turning the wheel has no effect.

I'm a bit stumped. Maybe I just need an alignment? The car doesn't pull perceptibly to either side. Tread wear is even so far as I can tell across all tires. Maybe I have a wheel that's out of balance? All my other tires are correct pressure.

My passenger-side rear tire is low on pressure (by about 6lbs) so I wonder if it could be this. I'll be repressurizing it tomorrow and we'll see if that makes any difference.

Any other ideas I should be exploring?