I bought a 05 325i recently and I am noticing a noise coming from the front of the engine bay. It sounds like a low wobbly noise, almost like a grinding noise. I've searched forums and YouTube and I'm convinced it's either the motor mounts, ac compressor clutch, or the belt tensioner. I've also noticed what seems to be an oil leak but I think it's unrelated. Please follow the link to the YouTube video I uploaded to hear for yourself. Please and thanks for your help, as this is my first bimmer and I'm a little lost.
The Youtube video unfortunately doesn't pinpoint noise - may be your serpentine belt tensioners. When was the last time they were changed? FCP Euro has a OEM kit for about $158 that provides both serpentine belts, two mechanical tensioners (and bolts if you have a hydraulic tenisioner - mechanical is preferred), and pulley. Pretty simple to replace - videos available at Bavarian Auto blog... if you have an automatic transmission, you'll need a slim 32mm fan wrench and fan clutch tool to remove fan (wrench is about $18 and fan clutch tool is about $24 - holds the fan hub while you loosen it - and it is reversed threaded...). As for your oil leak - is it at the left front (right front as you are looking at it from the front)? If so, it is in all likelihood the Oil Filter Housing gasket - they go at about 100K. Only about $4 but some labor to get to it. Need to remove the serpentine belts, loosen oil filter cap to allow oil to drain back into engine, unloosen steering pump reservoir (2 bolts), remove alternator, remove steering pump (hang with wire), remove the two electrical connectors to oil filter housing, and then remove the 6 bolts that secure the Oil FIlter Housing. Pop off the housing and you'll see the old gasket which will probably be very brittle and broken. Remove, clean area, and install new gasket and reassemble. Other issues you may have at about the 100K mark is the valve cover gasket and the crankcase ventilation (CCV) system... valve cover gasket kit is about $65 - will smell oil inside car when becomes brittle - leaks oil on exhaust manifold shield. CCV, also know as the PCV, is a bit#$h to replace - see my comments on this site at https://wiki.bentleypublishers.com/pages/viewpage.action?pageId=83329062.
GREAT video on bavauto blog on how to replace (go to Youtube and type in BMW e46 PCV replacement). Trick is to know when your CCV/PCV goes out - causes a lot of angst. Good write up on Bimmerfest on issue (read ENTIRE string - says e39 at beginning but they also discuss the M54/e46)... http://www.bimmerfest.com/forums/showthread.php?t=534005 - found the clear tube technique to check crankcase vacuum works great.