2.7 Humbuster Bracket

I changed the fuel filter and while I was at I removed that pipe brace that goes from the Intake Plenum to the left engine mount.
I didnt put it back on right away and drove it that way for a few days
I noticed this mid pitch pronounced bumblebee hum when backing off the throttle above 2500 RPM , sounded kinda cool like a rice burner drifter kinda sound
when I put the bracket back on it went away.
Much quieter now.
I was wondering what that was for, I figured it is to add support to the intake plenum, although it seems like it should do fine on its own, (unless a gorilla climbs on top of the motor and starts jumping) but now I am wondering if it was an engineering afterthought just to cut noise

barely discernable just in front of the starter :