I've encountered this nagging problem twice now, first with my '82 
Vanagon and now again with my '91 Westy:  A persistent, buzzing or 
rattling noise from the gear shift lever, when running in 3rd or 4th gear 
at about 2,500 -3,500 rpm.  It's particulary pronounced in 3rd gear, 
about 45-60 mph, where of course, due to general lack of power and a 
really limited torque band, I spend a lot of time.  The source of the 
noise <<seems>> to be in the vicinity of the linkage of the shift lever 
to the shift rod that runs back to the transmission.  In both cases, the 
noise only appeared after 15-30K miles.  

I've had the dealer (Carter VW, Seattle, WA - really a pretty decent 
outfit), go over the thing several times (on their dime, even though it's 
technically out of warranty!).  They've tried relubing the linkage, 
readjusting the linkage, realigning (slightly bending) the shift rod, and 
I'm not sure what else.  After there last attempt, the noise went away 
for 1,000 or so miles, but is now back with a vengeance.  I know this may 
seem petty, but this is an extremely (to me at least) annoying noise that 
can really detract from otherwise peaceful, serene travel.  Any 
suggestions on how I can correct this would be appreciated.