When my e36 is in neutral with the clutch engaged it makes a slight grumbling. Push the clutch in and select a gear and it stops. No weird noises (other than the failing power steering and rattly exhaust) while driving either. Not overly bothered because ill probably put some miles on it while I get my life in order, then engine swap it anyway. E46 323i are cheap here, sell some parts and I can get a low mile 2.5 i6 for less than £200.