I have a 1995 Sea Ray 400 EC, 454ci. mercruisers, Hurth ZF HSW 630 A-1 , 2.04 Ratio Transmissions. When cruising at idle (600 RPM) the starboard transmission makes an intermittent rattling noise. As soon as you increase the speed (800-1000 rpm) the rattling stops completely. The boat runs fine cruising at 3200 RPMS. I changed the filter, no chips, the fluid was clean. Should I be concerned ??