2003 Mazda 6 right rear wheel

I took my Mazda6 into the shop 2 weeks ago for a noise coming from the right rear wheel of my car. It makes the noise only when im accelerating. Almost like the sound of a rock in my tire. The guy at the auto shop told me he didn't hear any noise when he test drove it. I took a test drive with him when I went to pick up the car and sure enough there was no noise. As soon as I left the noise started up again. I drove a few days and the noise remained. I took my car back up to the shop and told the guy to drive my car for a day he would hear the noise. He called me and told me I needed a new right axal. Mine was shooting oil all over the roater and the back of my tire. So I had them replace the axal. I drove my car off the lot not hearing the noise. The next day the noise started up again. I don't know what to do now. Im afraid they will tell me its another part im supposed to replace. I know without driving the car it might be hard to tell what the problem is but could you please try to point me into the right direction.
Thanks,
Krystal