Don't panic as it isn't very common at the moment because most cars are still under 100k miles, but i bet u it will become more aparrent as the cars get older with higher miles. So if your looking at buying a e46 m3 with higher (even low miles) this is one thing u should check for and i will explain below how to diagnose the problem. A couple years ago when i bought my 1st e46 m3 it had this annoying rattle, which was more noticable in the higher gears between 3-5k. I took it everywhere including Sytner main dealers in brum (Stupid tech said it was engine bearings and engine was knackered because it had 130k on it!) with no success apart from being told it was vanos/chain tensioner/ ICV/ bad bearings etc etc. Their were tuners who wanted X amounts of money to investigate the problem but already knew what it was from the symptons. After 2 months of faffing about luckily a guy hit me and i got rid of the car. See this original thread about my last M and symptons it suffered: http://forums.m3cutters.co.uk/showthread.php?t=756 I have personally seen 4 cars which have had this problem and because off this recent thread below, i was reminded and thought i'd start this thread. http://forums.m3cutters.co.uk/showthread.php?t=8811 As mentioned before, the rattling is the car pinking (det) and as i used to mess around with jap cars i knew this sound but was a newbie to the s54 and kept getting told that they make all kinds of sounds. I even took my last M to a trackday at Donnington thinking it might be carbon but was baffled as i drove home and the pinking/rattling dissapered so thought this was true and all my probs had been sorted, but the following day the noise came back. Luckily as above got rid of that car. Anyway moving on a year or so i bought my current e46 M with over 100K miles. Everything was fine but after about 3k miles i swear could hear a very faint ratttle, similar to my last M but alot quieter. I only picked this up because i knew the sound from my last M and am very sensitive to iregular noises from the car. U will hear this nosie mainly from 3rd gear upwards with only about 1/4 of throttle pressed accelerating between 3-5k as the engine noise gets so loud u wont hear anything past the rasp. Funnily enough, if u boot it at FULL throttle it doesnt make this sound and what most people do when they test drive and think all is good. If u dont know what det/pinking is, basically it sounds like marbles being shaken in a jar or spoons rattling on top of your engine....not good! If u are getting pinking and no fault codes come, do a compression test. This will show u if any of the cyclinders are loosing compression as per the recent thread above. If u get 2 adjacent cyclinders with low pressure then u will most likely have a split their. If this problem i not rectified, it can screw the head up and that means $$$$! I have personally only seen this problem on cars over 100K miles including both mine and a mates vert. The gasket is very thin between the cyclinders only a few mm thick and with miles gets brittle and cracks causing loss of power and compression. The attachment is a pic of my mates headgasket, which he didnt even relise was cracked but i noticed when i drove his car. His was extremely bad and was cracked between almost every cyclinder becasue he had been driving it like that for the last 4k miles! His head was slightly warped so needed to be skimmed. I had mine replaced early, so head was ok and below is a list of parts i had needed for the fix. Parts needed to repair if head is ok from what i can remember: headgasket headbolts vanos gasket oil+filter coolant inlet and exhaust manifold gaskets throttle bodie clips .............................i had other few bits like chain tensioner/guide rails and oil pressure valve replaced because of mileage. It cost me approx £700 to get it sorted including labour by my Indy who i know very well. Was getting qouted £900-£1300 for the same job without the extra few bits i had done from some tuners and Sytner wanted to replace the fecking engine! I had my head de-coked/cleaned and then fitted and before my indy took the head off even he didnt think it could be the headgasket. So as u can probably work out, this is another potential problem which u should look out with higher mile cars. Fingers dead from typing lol!