Fixing noisy floorboards is a relatively simple diy job. There are several ways of curing the problem.
Brush chalk or talcum between tight-fitting boards that are rubbing against each other, or ...
Tighten loose boards by using 50mm screws instead of nails to grip the boards securely. Pre-drill the boards to stop the wood splitting.
Remember though that there may be cables or pipes below, so lift the board first to check this out. Generally speaking, services should be routed along the centre of floorboards, but this not always the case.
Floorboards with no support
If a board end isn't supported by a joist, take up the board and screw a 25x50mm batten to the side of the joist. Lay the board back on top of the batten and fix with screws.
You may come across a board which has been cut between two joists with the result that nothing is supporting the join. In this case, you can lift the offending boards and fit a length of 2x2 timber between adjacent boards to provide a bridge. Insert the timber and hold in place with a cramp while you screw the adjacent board to it. You will then have something to fix the loose end to with screws.