2004 Tacoma making grating/grinding sound

2004 Tacoma 4x4
2.7 liter 4 cylinder
manual transmission

When driving (any gear, most common 3rd or 4th) the engine(?) makes a grating/grinding sound at about 1900rpm. It only happens with minor acceleration or engine strain (going up a moderate hill) and sounds sort of like a fan.

About a month back I ended up doing some unexpected rock crawling on a backpacking trip, but I don't think I did any damage to the truck other than a couple of dents & dings.

Any idea what this might be? Should I be worried or get it checked by a mechanic? I need to change the oil and take it in for inspection when I get time this month.

 

you think its a fan? hmmm well maybe your engine mounts came loose or broke

happens to the 2nd gen 05's nd 06's
http://www.youtube.com/watch?v=-P22feMUdJ8

other than that

 

I just replaced my alternator and I'm having a similar sound. At first I thought I was dragging something metal behind the truck, so I stopped and realized that the sound must be coming from under the hood. It went away as I kept driving though, so maybe it's fine?
I'll report back if I find out anything.

 

My best guess is that it's coming from something that got knocked loose. It's metallic sounding, could be from vibration.