Back when I had a bug, the speedo cable would sing during the winter.  It
had to be pretty cold for it to happen, however (maybe below 20F), and there
was no doubt about the noise.  More like an alarm than a buzzer, and the
speedo would immediately drop down to zero while it was singing.  If it ever
warmed up enough, the singing would stop and the speedo would start working
again.

YMMV
Matt

-----Original Message-----
From: mordo
Subject: Re: What does the oil pressure warning buzzer sound like?

...Jus as an alternate theory, some on the Samba have suggested it's not the
buzzer but instead a cold speedo cable...