If the spring is touching the blade tang, it may need to be re-seated. Hubertus' are bad about this. The spring works it's way out of it's slot, but the blade does not let it come all the way out. Here is the repair: Find a suitable small screwdriver, nail, etc that just fits between the liners. Close the knife just a little past half way and insert the tool between the blade and the spring. Open the blade fully, keeping the tool under the spring. Force the spring toward the rear of the handle. Remove tool.
If the knife just needs cleaning, spray it out with WD 40 several times. Dry it thoroughly. Use a good oil on the pivot.
You may also need to depress the lever more fully.
Bill