The injectors are pretty loud on M42 but you can't hear them from inside the car... if you can hear ticking from inside the car its the Hydraulic lifters.
best thing to do is check the tensioner first, but if that not the problem then it's the lifters.. I replaced all of mine - it cost a bit of coin but the car no longer sounds like a lawnmower (well atleast a fine tuned one)
HYDRAULIC VALVE LIFTER - part# 11321734341 - price not from dealership $30.97
E30 Stuff For Sale: Clutch Fan and Shroud, 4 Pack Ignition Coils, ATE 750il MC (New), Offset Trailing Arm Bushings, m42 Valve Cover (Clean), M10 Engine Mounts (New), M42 Injectors,