That filter is probably the air filter. They usually have a remote filter and a tube coming off the control body, or the air filter is included right in the top of the control body.
I cant recall hearing any noises coming from mine while pumping, so you may have a problem with the hydrovac. As an added precaution prior to start up, pull the small plug off the rear of the power cylinder and add a little mineral oil or a thin non-petroleum synthetic oil if it doesnt dribble out of the hole. It only takes 1-2 ounces of fluid.
Jeff
