A couple of months ago I had noticed a vibration coming from my front end, or at least it seemed like it. Since I was planning to buy new tires in January, I sped up the purchase thinking that the vibration may be coming from the old tires being out of balance etc. The vibration issue has continued with the new tires despite three balancing attempts, so I'm thinking it's something else. Here are the complet symptoms as far as I can explain them.

1) The vibration is sporadic, meaning it isn't happening all the time. I have mostly noticed it at freeway speeds, but also occasionally lower speeds.
2) Today I heard and felt almost a "click" or "clunk" when the vibration was going on and it immediately stopped. It was almost like it was the clunk of going into gear, but this rig has a standard transmission--not an automatic.
3) I'm wondering if it could be brake related as I have been having my ABS dash light come on, plus, I have been noticing a little sponginess from the brake pedal occasionally.
4) I recently had a tie rod end replaced and no change from that at all.
My mechanic can't look at it until a week from tomorrow. Any ideas on what's causing this from my description?

Check for any worn out U-joints. If bad, install OEM only.. other brands are junk.

Check the u joints and play in the dive shaft.

Also check the slip joint for play up and down and twisting as it can cause clunking. Check the double cardon joint too, it has 2 u-joints and a cv joint thingy in the center.

I had a high speed vibration 65mph+ and clunk accelerating after a complete stop. Ended up replacing the driveshaft w/tom woods unit. Vibration went away.

Check the wheel bearings and ABS sensors since worn bearings can cause vibrations and a faulty ABS sensor might explain the light and spongy brakes. Also inspect the driveshaft and U joints for play.