Could be,
Ac pulley I've heard of seezin.
Could be a number of things though.
It's not coming from the pcv valve is it?
When I opened the bonnet it seems like the noise from the pulley side of the engine, also on the way to the garage this morning I can add lumpy idle with the rev counter unsteady at the traffic lights. Also, it runs for a fraction when you turn off the engine.
Hopefully the specialist can identify belt, pulley, or PVC this morning.