I have a Panasonic NV-J47 VCR that makes a buzzing sound through the TV speakers along side the sound of what is on the tapes. It does this with RF-out and SCART. It also happens regardless of the kind of tape used, tape speed the tape operates in, different RF/SCART leads and even different TV's

EDIT: Forgot to mention that the noise level increases when volume on tv is turned up and that it gets worse when using SCART

Any ideas of the cause?

Do you hear the buzzing sound, when the VCR is on standy?
Do you also get picture interference?
It sounds like to me (no pun intended) that the VCR's PSU is radiating interference in to the Scart/RF outputs.
I have seen and heard this type of interference before where it affected the sound,
but not the picture.
Try a different VCR if you have one.

expect to get a load of responses along the lines of " what are you still using a vcr for.... they havent made tapes for 10 years.." etc etc

How did the fault come on - did it suddenly start buzzing or just gradually got worse?

These G-deck-era VCRs are getting on a bit now, and collecting a few, I've had to replace nearly all capacitors in the PSUs recently.