Hi, we have an outdoor spa, water quality is good, but pump has just started to whine, not high pitch, just a low whine, we have checked the pump and no air escaped as we loosened the joints, turned it all back on and it was slightly more noisy, had to have a new pump 2 years ago after a burnout from air in the system, keep water levels high ever since, but have noticed on most of the pipes there is an oblong box which looks like it has a small plunger attached and held in place by a short removable stop, we haven't touched these, unable to send phot as it is the middle of the night here and haven't been able to sleep worrying about the spa