Do a search on this board - this has been covered in great detail. The problem is common to all GM tilt columns for most of two decades. A definite design flaw that GM never addressed. There are 4 bolts buried in the column that are difficult to reach. Virtually every GM column will suffer from these loosening sooner or later. It is very worth fixing of you DIY but would be pretty expensive if you take it to a shop - lots of man-hours. Regardless still cheaper than replacing the column which isn't necessary since once the bolts are tightened, the column will be like new.
It isn't technically hard to fix yourself but takes a couple of specialized tools (that you can easily make yourself) and guts to tear into the column. I am always amazed that GM stuck with this thing as long as they did in view of the design flaw and the man-hours it would take at the factory to assemble it in the first place.