Voltmeter & dash lights fluctuating

[brassmonkey001]

Sat in traffic on my way home from work tonight and I happened to notice the voltmeter needle moving left & right, about 3-4mm movement. I'd never really noticed it before but then how often do you sit and watch the voltmeter? So I watched it doing this for a little while and also noticed that the dash

[Jameswallace]

were you indicating?

[brassmonkey001]

No, I wasn't indicating. Wipers were off. There isn't anything switched on that would cause it that I can think of.