Vibration-shudder around 1800-2000 rpm

Two months ago acquired a 2007 Tacoma, 2.7L 5MT 4WD. About 147,500 miles now. When accelerating moderately in gears 2 - 5, there's a shudder type sound - hard to describe. Similar to heat shield resonating, but more like the drivetrain. It's only if I apply the throttle moderately - if accelerating gently on a level road I can usually avoid it. Years ago I had a 4 speed manual Dodge truck that was very similar.

It's only around 1800 - 2000 rpm. When on the highway the rpms are around 2350 at 65 mph - so if I accelerate from there it doesn't happen. Not too concerned about it - at this point not even worth having it repaired, I just wonder what it could be, and if others have experienced this.

 

I say vibration where the airbox goes into the fender, take it off and see if noise stops.
If it does replace the foam gasket around the flange where goes against the fender.

 

Maybe vibration isn't an accurate way to describe it, the noise is a coarse sound from the drivetrain, only present when accelerating at the mentioned rpms. So, typically it's just for a few seconds. I'll check the airbox, although I'm not completely sure what that is. Is it what houses the air filter? I did open it recently to check the air filter which surprisingly looks new.

 

Airbox sits on the pass. side fender right behind the washer res. 2 bolts hold it down, remove corrugated hose going to filter housing and then the bolts, you'll see the big flat ring against the inner fender where the air horn goes thru the fender.
On that ring you'll see what's left of the cheap foam gasket that deteriorates allowing the horn to vibrate against the fender at low rpm's, replace with better gasket type stuff and I'll bet it stops.


Mine did the same vib's sounded horrible and took almost a year to pin down.

 

I'll check it out, thanks.