If you buy a set of Mavic wheels you should get a set of three plastic tools with the wheels. There is a special spoke wrench for the splined nipples, a puck with slots that holds aero spokes stable when you turn the nipples, and a weird looking wrench that has some tiny round barrels sticking out of it. This last tool is for the hub adjustments. Most Mavic hubs, on one side (the non-drive side for rear hubs), have a circular disc with six holes in it. The little barrels on that tool fit into those holes on that disc on the hubs.
You adjust these hubs just as you would a threadless headset. Turn the disc clockwise until it binds and then back off about one eighth of a turn (or so). It's about as simple as it can get. If you don't back off enough, the bearings will bind and I think that's what you are experiencing. I think your mechanic knows what he is doing, but just got the hubs a bit too tight. Clicks, pops, creaks, and other strange noises often take several shots at diagnosis before they are properly troubleshot. Gotta be patient.
You can surely turn those adjustment discs without the special tool, but it makes it easier. If you bought the wheels at that shop, ask them where the tool set is that should have come with the wheels. It's possible that, if the wheels came installed on a bike that the tool set just did not make it out the door with your bike. I don't know the price for that tool set, but they are just plastic and should only be a few dollars.
As for your clicking noise, that's pretty hard to diagnose from where I am sitting. Sorry ;-(