Caution: The noises that occur when the seat belt is retracted are functional. If the noises are disturbing, only the seat belt should be replaced. Under no circumstances should oil or grease be used to eliminate the noise. The automatic seat belt retractor mechanism must not be disassembled, as this could cause the pre-compressed spring to jump out. Risk of accident!
Pull the seat belt out completely and check for torn fibres. Damage may occur, for example, if the belt is pinched or melted by a burning cigarette. In this case, replace the belt.
If there are abrasions without torn fibers, there is no need to replace the belt.
Check the heavy-running belt for folds; if necessary, remove the trim from the middle pillar.
If the automatic belt retractor mechanism does not function, the belt must be replaced.
Clean seat belt straps only with soap and water; never use solvents or chemical cleaning agents.
[The original text can be read on the website bmwman.ru]