troublesome issue

[Kerry Benton]

Hello all, 
Recently my car has had the following problem...

i get the warning light with the red emergency triangle and the word "BRAKE"
across it.  According to the manual this is either a) low brake fluid b) low
hydraulic fluid or c) a problem with the brake system in general.  

I've checked a and b and both levels are ok...  additionally, the symptoms i
seem to recall are usually associated with those things (increased stopping
distance, pedal travel, etc.) are not present and the brakes feel as they
always have.  As for option c, while possible, i expect that this would also
have shown up as a different feeling brake, but not necessarily, i know.
Plus, the entire brake system (master cyl, calipers, rotors, hoses, etc.)
was replaced about 3 months ago, so that isn't it (at least i *really* hope
not).

Now for the really confusing part (for me, and i admit to not being a guru
at all when it comes to cars).  The light only comes on when i'm going 70
mph (or, i assume, faster, but i don't really drive much faster than 70 very
often).  For the past few days i've been going 65 max and it's not come on.
This morning as a test i pushed it up to 70ish and the light come on almost
right away.  I then kept it slower for the rest of the 25 minutes of the
drive and didn't see it again.
 
On the one hand this seems pretty serious, but I haven't noticed any further
issues, so I thought before I potentially blow a bunch of money on a
mechanic, I'd ask some other knowledgable folks...

If you can help, please email me directly at krb1 at email.com.

I appreciate it.

cheers,
-kerry