NOISE COMING IN THROUGH AIR VENTS

I own a 2002 honda accord 1.8SE, 65000 miles, I only recently purchased this car, the timing belt was done when I bought it but after 2 weeks I had to take it back in to have the clutch replaced. Now there is a noise that seems to be coming through the air vents. It is quite loud and getting worse as the days go by! It doesn't sound like a rattle more a dull but loud noise. I took it to a mechanic who seems to think its coming from the distributor, but when I took it back to the main dealers where I bought it from they said they couldnt hear anything! What do you think could be the problem?