my car has about 1200mi and I started hearing the same thing (jet sound, very subtle) not a concern at this point
I only noticed it after I lowered the car, (pro kit) could just be timing?
I replaced the orig. panhard bar with an adjustable alluminum one with rod ends at same time
could be (for me) the higher spring rates and solid mounting of bar made the allready present noise more pronounced
also, besides the rubber mounts on stock bar, it is filled with some sort of medium/beads likley for dampining reasons, anyone else who removed (heavy) stock bar notice this? (if so, post mfg. date)
there has been a TSB for rear end noise I think, the fix is a dampner installed on axle, maybe on later cars like mine they solved the problem by using a bead filled panard bar to isolate noise/vibes