Hi,

Over the last month or so, I've been hearing a loud and very noticable whining sound coming from the engine when accelerating from a standstill. The whine gets louder as the RPMs increase. The thing is, it doesn't always occur and when it does, it's usually when the engine is warm after I've been driving for at least 20 minutes through both city and highway traffic. If it was consistent, it would be easier to diagnose but the fact that it's random leaves me puzzled. Could this be a vacuum leak of some sort? What should I check?

Cheers