Renault Clio 1.2 Dynamique 2002 engine noise?

When driving the car, on acceleration I can hear a noise that sounds like the exhaust blowing.

I asked my dad to listen to it today as im female and he said its not the exhaust, he lifted the bonnet up and took off the plastic cover from the engine.

The noise then sounded like a sucking noise coming from the engine compartment, my dad then kept putting his hands over parts while i reved the engine on and off.
No noise at all when engine is just idling but when reving or driving the sucking noise comes back.

has anyone any idea what could be causing it?

angi
July 2008