I have this strange fluttering sound from what seems like the lower front drivers area when accelerating hard (under load). I believe it makes the sound at all RPMs but its mostly noticeable in lower RPMs where the engine kind of bogs especially if you mash the gas..

It sounds like air? But I'm not finding any leaks.. thought maybe its the timing chain? But I dont see any evidence of that really under the valve cover..

Can hear it in this audio/video I recorded if you ignore the exhaust sound..

 

What year 22RE? How many miles on the truck? How many miles have you put on it since you bought it? Ever changed the timing chain since you've owned the truck?
Toyota recommend the timing chain be replaced every 90,000 to 100,000 miles.

The timing chain on a 22RE isn't under the valve cover, it's under the timing cover on the front of the engine. Use a 3 foot length of tubing or garden hose to your ear & point the other end at different places around the engine while it's running. You can pinpoint the area where the noise is loudest, & give yourself some idea of what part(s) may be causing the noise.

If the noise is on the lower drivers front of the engine, it could be a stretched (worn) timing chain, a slack chain (again due to stretch or from the tensioner being fully extended & unable to take up any more slack, a malfunctioning tensioner (kinda rare), or a broken chain guide on driver's side (well known to happen with the plastic backed guides), or any combination of these.

If you have a slack chain it will be louder at lower RPM's. The noise will (usually) lessen as engine speed increases. If the driver's side guide has broken, it's important to get that fixed sooner rather than later. With the guide broken the chain can eat through an area inside the timing cover into a coolant passage, which can then dump coolant into your oil. Not good.