All tubes are microphonic to some degree. Direct-heated tubes are microphonic to a greater degree than others. There are lots of ways of dealing with the issue, mostly involving adding mass. Making the tube envelope heavier with the flask weights Dan has written about is a good idea. Also, some people like to leave out the silicone O-rings packed in the kit. If you are one of those people, please put them in, they help a lot. While a little noise when touching a chassis may seem like a huge deal, remember that the point of this gear is to put on music and listen to it. Relax and enjoy rather than poke and worry!
If it is going off when you walk by, then I'm going to make an educated guess that it is on a floor standing piece of furniture, and you aren't on a concrete slab floor. If you have the ability to use a wall mounted shelf instead, that will help tremendously. If not, try adding some mass to your stand. Also if possible, move your stand, as it could be on a particularly bouncy part of your floor.
Finally, tubes need to break in. Give it at least 50 hours of run time before deciding it isn't working. Additionally as a tube warms up (i.e. in the first half hour or so after turning on) it will make more noise than after it has reached its operating temp.
