I did think about the spark plugs but when I Drive the truck it runs fine and accelerates fine. I would have assumed that if he spark plug was loose the truck would only run on 7 cylinders. But since it's an easy check I will check the spark plugs tomorrow and let you guys know.

Perhaps just maybe you developed an exhaust manifold leak. Not uncommon at higher mileage. Why are you scared to have the vehicle checked out by a reputable repair facility? Obviously something is not right.

I'm scared of the possibility that a trip to the shop will cost me my other arm after spending a leg during christmas...lol.

What is extremely odd (and making my head hurt) is that even if there was an exhaust leak, the sound of the leak would be heard at all times even when the X5 is idling. The exhaust leak sound only happens when it is rev'd up or under load while driving. Cruising around, it's quiet.

That's great info. Exhaust leaks are always there and get louder as rpms increase. Further, the sound as I hear it does not sound like an exhaust leak. Finally, since the sound wasn't there before you changed the intake manifold gaskets and it was there when you started it up directly after you finished your work, and to do the work the exhaust is not tampered with at all, I don't think it is an exhaust leak.

Engine sounds are often difficult to pinpoint. As previous suggested, I would purchase a spray can of starting, carburator or MAF fluid and sparingly spray it at the base of the intake manifold runners. The idle will increase when the fluid is sprayed near the leak. Also spray near any vacuum hoses that you could have disturbed. Any open tube that you can hold to your ear and move around the engine will very likely pinpoint the noise, even if for some reason it is an exhaust leak.

Might also help--why did you replace the intake manifold gasket?

I replaced the intake mani gaskets because since I had to remove it to find my oil leak, I might as well get new ones on there. Are they re-useable?

I spoke with a buddy of mine and he said he has used Seafoam to find leaks. I watched a few youtube videos on it, and honestly its terrifying to think about putting liquid into my engine like that....but it seems like people like it.

Some use Seafoam to clean the engine internally. Some would never use it. I use Techron in a full tank of gas once in awhile and always buy gas that contains Techron. I have not used Seafoam to find leaks and don't recall anyone mentioning doing so.

So I decided to stop by the dealer and ask them about my problem. When I told him the work I did on it he said that the X5 was making the sound because I did "use BMW brand gaskets and spark plus."

I had a WTF face on, smirked, and let the dealer!

Gaskets: Victor Reinz
Spark plugs: NGK platinum

Is the BMW guy high????

Another thing I noticed while trying to diagnose it is this:

If I rev up the engine slowly all the way to 4k, it does not make the sound....if I just quickly hit the gas, it does make the sound.