Try a couple of elimination points first.
Jack up and axle stand the rear wheels and let the hand brake off.
give the rear wheels a wobble test by gripping the inner wall of the tyre with one hand and outer wall with the other at 12 to 6 o'clock, then 9 to 3 see if there is any play. You are pushing an pulling towards and away from you... A healthy bearing will have no movement.
Next to try is using a marker pen and make a mark on the rear strut at exactly the same point as the highest point of the tyre. Now keep your eyeline on this mark and tyre and spin it... watch for any hopping up and down which would indicate a slight buckle of the wheel.
Next, take the wheel off and check the rear brake guard isn't catching anywhere, they can be easily bent in by mistake while working on brakes.
Double check the inner edge of the wheel itself... Sometimes a tyre fitter won't use the stick on weights on the large flat area but rather on the inner rim edge. This ends up catching slightly on things like hand brake cables, flexible hoses and sensor cables etc. and gives a slight "whump, whump" sound that is similar to a flat or low pressure tyre. Look for bright marks on the wheel and balance weights, it's a tell tale sign.
Get a long pry bar and place between the suspension links and give firm but gentle pressure just to make sure all the bushes and bolts are tight as they should be.
One last thing that might seem silly but believe me it can make a racket... The badged centre cap... Give it a tap, is it loose and gives a plastic rattle?
Remove it and take it for a test drive without it on. See if that makes a difference. Usually down to damaged plastic spiggot lugs and a loose spring ring on the cap.
Just out of interest what type of alloys are you using?
Aftermarket alloys and wobble bolts need plastic centre bore spiggot rings to settle on the concentric hub lip correctly, sometimes they can get damaged by "tyre monkeys" who can be a bit rough with them... Combine that with wobble bolts and the wheel could be wobbling slightly even though tightly nipped up.
Try those tests and let us know what you find... worth a try, it's all free
By what you have mentioned about the tread pattern it is certainly possible for it to start making a noise while starting to wear in a different direction, especially if the rear alignment has been adjusted. I.e. feathering... It takes at least 1000 miles for a previously feathered tyre to even itself out. The tyre can have even wear in mm of tread but instead of I_I_I_I it can have peaks like /_/_/_/.
Give it time if none of the above checks throw up something obvious
Hope this helps.