99 EK9 TypeR

hi all i have a problem with my ek , i did a 5-lug conversion and when i drive the car , going about 20mph the car has a weird noise kinda hollow sound coming from the rear , it gets louder when i go faster .... , so i lifted the rear end up and spun each wheel , they spin fine and everything with no noise ... now i'm wondering what it could be , at 1st i thought it was the tires i had on the type r wheels , sounds the same as tires that need to be balanced.... but i got all 4 new tires mount and balnce but still the noise is there ... one of my friends told me that it might be the dust shield but i push it back out of the way , what else could it be ??? took it to a mechanic and he told me i needed to change the rear bearings... told one of my friends that and he said no might be my hubs , oh and i bought this conversion from someone that said it was from a wrecked itr.....
what do you guys think , the noise really bugs me ..