New Ford Cougar owner 2.5 V6

Regarding the moosing... I always thought that was caused by coking from the EGR. As in, blow-by gasses deposited carbon in the valve.

And that was true for Tiger (my first V6). Flushing the unit with brake cleaner definitely stopped it...for a while.

But Sally - who doesn't have the EGR system - has started doing it now, at certain revs and very specific temperatures. So I think that the valve-cover breathers are just as guilty, dropping poo in the inlet. I've got an oil change in the near future, and will flush those hoses out at the same time.
 
Harmonic resonance, usually between the bellows and EGR but as Chris says that gets bypassed on the non EGR versions, so probably between engine pulses and intake chamber resonance, although thinking about it none of mine did it after i fitted a K&N, so that has an effect too