Speedo noise in 71 911...

[speedo]

So I started to hear a whine from my dashboard while driving which increased with RPM. I thought it might be an errant seatbelt buzzer at first, but no. I pulled over and the sound went away. Started driving again and it gradually came back. I put my hand to the tach and then to the speedo, and the sound and vibration was definitely coming from the speedo....which still appeared to operate correctly. Drove another mile and parked it. When I pulled the speedo out of the dash and disconnected the cable, when I drove the car again the sound was gone. So the cable is the cause of the problem. Anybody heard of this?
I had already noticed a very minor swepco leak coming from the speedo elbow on the trannie and figured I would need to replace the O ring on the elbow. Now I am wondering if the two are related. How would a leak past the O ring affect the cable and/or performance of the speedo?

[Trackrash]

Oil the speedo cable. Oil it on the upper end behind the dash. Allow the oil to soak down the cable housing.

[speedo]

Ok, pulled it out and fed the shaft a healthy dose of WD 40.
We'll see how it goes...wonder if I should lube up where the shaft/drive goes into the speedo?

Thanks

[The cap'n]

WD40 is a poor excuse for a lubricant, and its success in the marketplace is a tribute to the power of advertising over substance. Get some Tri Flow and do it right.

Now, on to the meat of the issue. If you disconnected the cable from the instrument, and the sound went away, why would you think the cable was at fault. The ONLY thing you removed was the speedo, NOT the cable. I'm inclined to suspect the instrument, not the cable. Unless the problem is in the integrity of the connection between the cable and the speedo itself, a noisy cable is pretty likely to stay noisy, connected or not.

The Cap'n

[speedo]

The WD 40 did the trick. No more noise and both the speedo and cable were happy. Me thinks that When I restored the car, some media from the sandblaster snuck into the sheath on the speedo cable. As I started to drive it...the media made it's presence known. The WD 40 was enough to remedy the problem. I didn't realize it was such a poor excuse for a lubricant. I will look into tri-flow in the future...but I still think that WD 40 has it's application from time to time.
Thanks for the responses.

Speedo