Occasional steering wheel vibration

On rare occasions, my steering wheel will vibrate after getting up to and above about 40 mph. It's the same symptom you would get if your tires were out of balance. It is minor though and it goes away in about 30 seconds. It only happens on occasion, and it drives fine otherwise. It rides nice and smooth, and I also don't have any wheel pull as if it might need an alignment. That is fine too. Tire pressures are good. Brakes appear to be working normally. (all four brake shoes and pads were recently replaced, and rotors resurfaced). What could be causing this to happen just here and there?

 

If it only happens rarely and you can't easily replicate it, maybe it could be something like steering rack bushings being worn out or the steering rack bolts being loose? Just thinking out loud. Not sure but good luck finding the source.

 

Tires flat spotting? Does it happen when the truck sits for a week or so?

 

No, I drive my truck daily. The vibration actually happened this morning but quickly went away. It does this whatever the outside temperature may be too. It's rare this happens though. I plan on having the tires checked out/ balanced soon.