Ever since I picked up the STI 4,000 miles ago, I noticed a humming
sound from the tires that is loudest at exactly 80MPH. At 90, a 2nd
different and quiter humming sound starts up. I took the Service
Manager on a test ride and showed him both sounds and he thought they
were normal. The 80MPH sound changes when the wheel is turned
slightly either way. Then, I put the snow tires (Dunlop Wintersport
3D) and snow wipers on. The 80 MPH sound is now gone. The 90 MPH
sound remains, but seems to be coming from the rear now. At
somewhere between 90 MPH and 120 MPH, a new, much louder sound has
appeared. It doesn't happen all the time, so road surface may have
something to do with it, but it has happened on two highways. It is
very loud. The only time it happened at a speed as low as 90, was on
a very windy day. It is a droneing sort of sound. Usually, to make
it happen, you have to go up to 110 or more, but once it starts,
slowing down does not make it go away until you drop to 90. I'm
thinking it is the side glass on the passenger side bowing outward at
speed; made worse by strong crosswinds on that one day where it
started at 90). There isn't really a wind leaking sound though. I
don't think that window/door fits right. (the door feels like it
hangs up and drops 1/4 inch as you open it. The lock looks aligned
and the door and glass look aligned though. The Subaru mechanic said
it was the trailing edge of the glass sticking to the rubber and he
lubricated the rubber. (this new loud sound only started after he did
that, but I'm not sure if it started before or after the snows went
on since I may not have gone 110 between the lubrication and when the
snow tires and wipers went on) One of the reasons I'm thinking
glass/door issue instead of tire is that the noise is very
inconsistant (it changes a lot at a steady speed; maybe with gusts of
wind?) and it doesn't go away or change when you take your foot off
the throttle until the speed falls to 90. The easiest thing to try
next is to put the regular wipers back on, but I doubt that is it.
In the Spring, when the snows come off, it could go away. I could
talk to some tire people to see if inspection of the right front tire
(where the noise seems to be coming from) could reveal a problem. It
looks fine to me. As hard a time as I had to get someone to come on
a test drive with me at 80 MPH, I don't think I will ever get anyone
to go 110. My biggest concern is just the possibility of a tire or
wheel bearing failure at speed, since I don't actually stay at those
speeds for very long. The tire wear looks fine on both sets of
tires, by the way.