Oracle Database Discussions

Hi
on our prod.db since y'day this event is there for one particular user.when we are monitoring we found that the
os user id randomly with oracle user name/schema whatever is used in our prod.db it took with any oracle username with this particular os user name and in always displays this wait event .when i killed this n number of times immediately it came no sql id it generated suppose if we kill next time it came with another oracle username and same osuser without sqlid we could not trace the sqltext also. i dont think is anything running from that (osuser) PC.eventhough he closed his session and not using that id also. still its showing (osuser )with most of the time this wait event. i tried to enable oradebug session trace it usually generates the file in user_dump_dest but for this id it generates from the background_dump_dest. yet to find the exact reason what would be the reason?
if anybody came along with these types of problem i think oracle either(sys) or anyuser executing internally something .. strange. pls any help on this.

Thanks
M.Murali..