heater causing rough(er) idle

Hi,

When the heating is on (I use the 'soft' setting), resting my hand on the steering wheel I can feel the kind of vibration associated with idle being not the smooth.

Nothing terrible, it's just with the heating off I can not tell by if the engine is on or not, but with the heater fan on it can be felt very much.

I'm guessing it must be the extra electrical load associated with heat being on - is there anyone else with similar symptoms?

I'd say it's unlikely it is caused by the fan bearing or anything like that, as there is no vibration near the glovebox area, I can only feel it on the steering wheel.

thanks,

T.