I got this lens second hand from eBay; it was in perfect condition, but recently when I zoom in to between 135 and 200mm it makes a grinding noise and shakes.
Does it still have problems with IS disabled? - some users report the problem only with IS working.
LENS RENTALS publish lens failure data here and report
This Yahoo groups discussion re problems with Nikkor 70-300mm f/4.5-5.6G IF-ED AF-S VR Zoom sounds similar to yours. The majority of users report problem free operation - even after accidents in which the attached camera was destroyed, but three (+?) users out of under 20 in the discussion report problems that sound like yours.
Lens service manual here for $4 - PDF - may suit yours.
More information would be needed for specific analysis.
I have seen lenses misfocus in certain zoom ranges due to a bad zoom sensor. The sensor "tells" the camera what focal length the lens is set at - often by using a multifingered Gray-Code sensor. If one finger makes poor contact the lens may become confused and hunt forever when in certain ranges affected by that Gray-Code bit. Such a fault is relatively easily fixed BUT still needs lens dismantling.
How long have you had it?
DIY?: Depending on what the lens cost, and what it costs to repair it may not be commercially repairable. If so, you may be able to obtain or buy the relevant Nikkor service manuals, and if you are mechanically skilled lens dismantly with no instructions is often doable. In many lenses you can perform basic dismantling to the stage where you can access drive mechanisms without disturbing the relationships of he lens elements. Realigning lenses-proper involves forms of the black art not found in most home workshops. I have had some successes and some failures in doing this myself - and the failures were worthwhile as the lens was valueless as-was and not viably commercially repairable - and the failure provides good experience for "the next one" :-). .
Here is a Nikkor tear-down discussion - it is NOT for your lens, but gives an idea of the typical things that are involved.