Newbie Shimmy Question?

I've read tons of discussions on the forums about shimmy problems. I've talked to my LBS with not a lot of resolution. So maybe someone could give me some advice?

I've been riding for a little over a year and have been through three bikes. Trek 2200 for a month or so. Then a Cervelo Soloist for about 10 months. Then I decided to go with a custom built Seven ID8. I got the bike in May and have put over 1000+ miles in so far. Up until several weeks ago the bike has been flat out PERFECT! So solid I would feel comfortable descending at 40 mph with no hands! Then, a few weeks ago I started to notice the front end felt "different" but couldn't put my finger on it? I took it into the shop and they said my Reynolds Attacks had a defective hub and sent back to Reynolds for inspection. They gave me a set of Mavics to ride while my wheels are back at Reynolds. I've ridden the brand new Mavics for about a week and still notice that my front end feels unstable at times. The bike still handles fine and everything seems to be functioning correctly, it just feels less stable particularily on decents. If I'm in the drops and give both hands a quick short left/right shake it feels like I could snap the wheel off the forks (hope this describes it okay?) I never remember it feeling like that....always rock solid up until a couple weeks ago. I also notice if I take one hand off the handlebars the front end feels unstable and wobbly. The thing that has me concerned is I've put a good bit of miles in on this bike and I know something feels different. The shop mechanics think I'm over analytical and everything is fine. However, they've done no further inspection other than sending the Reynolds wheels back (which they love because they didn't want me to get them in the first place).

So any input? Could there be something wrong with the Chris King headset? Any suggestions or feedback would be GREATLY appreciated! Thanks!!!