The pump on my 24v is making a rattle that is noticeable when driving particularly under light load and lowish revs. Pump was refurbed about 6 months ago. When I pump the primer on the filter housing the rattle disappears but comes back again after 5 or 10 seconds. Local old school knowledgeable chap is convinced there's air getting into the pump, probably from the feed side, what does anyone else think?