63 Reg Bmw 120d coupe rear exhaust delete

Would a rear exhaust delete on my 120d coupe E82 63 reg do anything to the Turbo because of no back pressure and it has a K&N filter on aswell, it had a buzzing noise which goes up and down with revs I changed waterpump it wasn't that the noise is coming from the side the Turbo is on no dash lights no change in the car at all its annoying more than anything and would like to try know what it is before things go tits up, its sounds like an electrical buzzing noise but some people say might be a bearing noise so any help would make a difference thank you