Wheel balancing

[sgt_doofey]

Hi all,
I took the Pug in to our local tyre place on Wednesday for a wheel alignment and balance. We had some vibration in the steering wheel prior to the balance and you could hear the tyres are out of balance at higher speeds.
Now, they did the wheel alignment and said they weren't going to bother rotating the tyres as the front ones are probably the better ones out of the four. They then proceeded to balance the front two tyres and I was on my way again. No more vibration in the steering wheel anymore.
Now, driving down to Adelaide this morning, we can still hear the noise coming from the rear of the car. So it's possible the rear tyres are out of balance.

My question really is this: On front wheel drive cars, do tyre places only balance the front two tyres, or should they be balancing all four?

The car is only 30,000kms old, so the wheel bearings shouldn't be stuffed, so that shouldn't be the noise. It does sound like a regular sound that increases with speed, sort of a whump, whump, whump, etc. The rear tyres were the front ones, but they were rotated on to the back at 20,000kms.