Strange noise coming from my engine

It happens when the RPMs are generally below 2000 and also once the car is warmed up, not when its cold. It does this especially when its hot outside too. Despite this, the car has been running good for the most part other than it burning some oil every now and then. Does anybody have a clue what it is? One more thing to note, i did notice on hot days if i start the car (once its been warmed up too) the RPMs will suddenly drop and i have to give it a little gas, but once i start driving it won't do that. I think that might be just a vacuum issue though.

Heres the youtube vid: http://www.youtube.com/watch?v=1OvoXkPDiKY

It happens when the RPMs are generally below 2000 and also once the car is warmed up, not when its cold. It does this especially when its hot outside too. Despite this, the car has been running good for the most part other than it burning some oil every now and then. Does anybody have a clue what it is? One more thing to note, i did notice on hot days if i start the car (once its been warmed up too) the RPMs will suddenly drop and i have to give it a little gas, but once i start driving it won't do that. I think that might be just a vacuum issue though.

Heres the youtube vid: http://www.youtube.com/watch?v=1OvoXkPDiKY

if the engine makes noises when hot out must chect the exact temp, and the exact oil pressure....this is the start point...

I have seen low oil pressures cause strange piston noises,,,also if the engine is running on the hot side the pistons will rattle...pre-ignition...
especially if the carb is set tooo rich...

I heard your noise that you made available....I never heard that before....It may be the air pump,that goes to the check valves on the exhaust manifold....this air pump is not supposed to pump after the engine heats up...also the check valves could be bad causing exhaust gases to get into it..

get a hose and with one end by your ear probe for the noise location...

Sounds like the divertor valve and air pump is going bad. Disconnect the belts and see if you can isolate the problem. Air injection check valves have been a source of this noise as well.
A stethascope probe/ hearing aid could help as well.