My Z-S fiesta started vibrating on the motorway on sunday between 70-85 mph. I assumed it was the wheel balance and thought nothing of it.

Today I had the tracking done and wheels balanced ( £45) and it still does it it does it in both 3rd 4th and 5th gear so it doesnt seem rpm related.

What can I do? The brakes dont rub either. I live in Dudley, is it worth giving the guys at Zoo a call to check everything is alligned properly if they do such crappy jobs? or shall I take it back to where i had it done and get them to double check first?

What else could it be if it wasn't wheel balance?