Strange (not necessarily bad) vibrations

[Notanutter]

The ride on my V8S is generally very smooth, and certainly loads better than my previous "S"s, but when I lean back against the headrest at say 40-60 mph I can feel what seems to be a sideways vibration through it (the headrest that is). Nothing obvious like a rear wheel falling off, any ideas ?

[z_chromozone]

You have probably reached the natural oscillating frequency of the seat

Have you checked some of the balancing weights havn't fallen off your wheels.

Z

[Notanutter]

Sounds plausible, thanks. Am about to have the wheels lightly refurbed, so once completed will do a proper balance.