<VV> putt-putt-putt noise

[Steven J. Serenska]

VVers:

My '65 Monza 110/4spd is beginning to make a noise that sounds like one 
we used to make as kids when we were trying to imitate a farm tractor.  
I'm not sure how else to describe it, other than you grit your teeth and 
blow air through your cheek until it sounds like a Model T putting along 
the street. 

(In order to make a preemptive strike against several of the VV 
humorists, let me emphasize that this noise is made by blowing air 
through the cheeks on one's *face*.)

The noise seems to be coming from the driver's side (i.e., away from the 
stock muffler).  It is in addition to the normal engine noise, and seems 
to accentuate when accelerating (e.g., turning onto a new street and 
coming up to speed from 2nd or 3rd gear).

It's subtle right now, but I'm planning on taking a 500-mile trip in a 
few weeks and I'd like to keep my eye/ear on it.  Is it possible that 
the exhaust gaskets/donuts need to be replaced on the left side?  Is 
this an issue with lifters?  Something else?

Any and all suggestions are welcome.

Thanks.

Steven J. Serenska