Rattling steering....

I have a 2006 prius - Package 6, Seaside Pearl, we picked it up near the end of january this year....

The weekend after the recall notices were mailed, I had an oil change at the dealer and asked them to check if it was one of the recall cars since My notice wouldn't have arrived yet. They did the oil change and checked, telling me it wasn't part of the recall.
Never recieved a recall notice, figured all was fine.

But as time went on, what I thought was my imagination became more common... I'll feel a slight 'shudder' in the steering wheel. Like something is slipping or rubbing in a wierd way.

The next, and most recent oil change, we mentioned this, and their first comment was on the recall, but then verified again that my car wasn't one of the 'effected' cars. They 'checked it out' anyhow, and couldn't find anything wrong with the steering.

Since that oil change, I've been paying keen attention to when it happens. At first I though it was only on turns. Today, I was proven wrong. I spend about 45 min in stop and go traffic on a fairly straight road... this morning, it did its shudder off and on for 5 minutes straight. The whole time, I was going a top speed of 10-15 mph, on a straight stretch of road. I believe it was in electric mode the whole time.

The best description I can give is that it feels like there is something 'slipping' or 'rubbing' wierd, like the power steering is trying to grab on and 'help' turn the car even though I'm not turning. I'll feel a gentle tug on the wheel, but its not so bad as to cause the car to actually turn.

I put in another call to the dealer today, and am awaiting a call back... I'm just wondering if theres anything more 'technical' you guys might think of that this describes that I should tell them? Its not a consistant thing, it happens once or at most twice in a day and I cannot 'make' the car do it, it just happens. So I can't necessarily recreate the problem for the mechanic.

I just want to get this fixed before something worse happens, like the steering failing altogether... :?

(Edit to fix package # now that I went and double checked.)