Tire Thumping

[Roadking]

I've noticed this vibrating/thumping at highway speeds and a sort of sideways wobble at 5-10 mph lately. I just had the wheels rotated and balanced about 500 miles ago. So, last night I jacked up the back wheels and started turning them around as fast as I could and discovered flat/depressed area on one of the tires.
These are BFG Long Trails that I've had for 42K and are only about half worn. I hate to buy one new tire at this point, I'm wondering if this a situation that will keep getting worse or is it dangerous to drive on it at this point? I'm guessing it won't get any better.
The Rocket Scientist sitting next to me said "just fill'em up with more air" they get rounder. Right! I'm thinking he's more dangerous then the tire?
Any one ever drive on something like this for any extended amount of time? or have this tire problem?

 

[DeRocha]

Where exactly is the flat spot (tread, sidewall etc..)? Do you have a warrantee on the tires?

 

[Roadking]

It's right on the tread of the tire, about 5" or 6" long.
I would image they come with a standard BFG 50K pro-rated warranty, I don't think that'll do much at this point. I'm thinking I can't just replace one, especially on the rear. As small as it may be I'll have two different diameter tires?
(Rocket Scientist just confirmed this with hand gestures!...man, nothing gets by him)

 

[DeRocha]

Bring the tire back to where you bought it and see what they say. How do you get a flat spot on a tire? I had a blow out with a BFG TA. It was 5yrs old w/ 45K on it (but a good amount of tread left). I brought it to sears (where I bought it with road hazard warrantee). I exected them to say it was to old and worn etc. To my surprise the credited $95 back to me...

It is better to have a bad tire in the rear than front...A rear tire blowing out will not effect handling as much as a front tire..

 

[Roadking]

When I said it has a flat spot, I should have said it 's more out of round.
As I spin the wheel it looks fine for 95% of the circumference then it has this slightly depressed area.
I'm amazed that this doesn't throw the whole wheel more out of whack at highway speeds?
Does this sound like a ply separating?