Difficult to say from where it's coming from. As I wrote I have to drive around to hear it (it needs some load to be noisy).

I tried with a friend putting some load on the engine while the car wasn't moving (hand brake, playing with cluth and throttle pedals) and I would say the noise is coming from the middle of the intake manifold (?).

I removed both belts to see if it was an accessory, but the noise didn't change.

If it was a bent pushrod would I hear it from idle? Or is that something that comes up at a certain RPM?

I posted the noise here:
http://videos.streetfire.net/video/ec2160b4-470d-4426-b420-ddc71ffb0c0f.htm

(it's from a small camera I put close to a heat extractor of my hood, so you'll hear almost every possible noise, I also have 36 lbs Bosch injectors that are noisier that the stockers).