Weird "Thumping" Noise on Highway...(1999 Ford Escort LX)

Hello,

Here's what I'm currently driving:

1999 Ford Escort LX
88k miles

Basically, I had some issues with the tires over the last month (two blowouts and a flat), so I had all four tires replaced. The next day, on the highway, I noticed a strange "rubbing" or "thumping" sound. It sounds like someone is dragging heavy furniture across a floor or something similar. The noise only happens when my car has reached 70+ miles per hour. The sound comes from the front of my car, near the firewall and vibrates a bit through the counsel. It is brief, maybe half a second long but it repeats every 10 seconds or so. (I counted). The car otherwise drives perfect. The transmission shifts flawlessly, there is no loss of acceleration (it usually happens at cruising speed), and I have even had the drive belt, tie rod, and tires replaced recently in the hunt to find this noise.

So, any ideas? I greatly appreciate any help.

Thanks!