3.4 V6 - in a 2000 Tacoma, California Spec exhaust
The sound is pretty hard to describe, but it's very obvious. Even my mother pointed it out with a "what the hell was that?". But it happens in every gear somewhere around 1700 and 2050 rpm at medium throttle. It's the most obvious when there is some more load on the truck - say I'm going up a hill and trying to accelerate. Now here is where it get's a little bit weird, when your're light on the throttle it does not happen at all. When heavy on the throttle it seems dependent on the engine load if it wants to appear or not.
I ran some seafoam through the intake which fixed what seafoam usually fixes. Pulled off the connection for the TPS sensor. In the past 6 months I cleaned the throttle bottle, MAF sensor, and I have confirmed that the O2 sensors are functioning correctly. The only thing I'm thinking it could be, and I have no idea how to check this is that there is a baffle in the exhaust that is vibrating when the correct amount of exhaust gases are moving past it.
Anyone else have any ideas?