I was out helping the new operator grease his 311 and noticed the thumb cylinder "whistled" when you opened it. It acts normally, doesn't drift or jerk. I'm assuming fluid is squeaking by somewhere but don't know if it's something to worry about???
Are you sure that it is in the thumb cyl ..... or is it in the valve bank ? .... my thumb on my 312 make a similar sound, but it is because of where we set the relief pressure at, to slow the flow down so that it wasn't to jerky ....just a thought .... I don't think i'd worry to much about it
ooops ...just another quik thought but if its at the cyl they could have put an inline flow restrictor at the hose fitting connection ...
There is some kind of ball valve on the stick, I don't remember what it's for. Maybe turning it on and off will do it.
Try post a pic of it .....could be its part way turned acting like a flow restriction and making it sound like a whistle ...LOL
if you have a ball valve on the stick that controls the thumb, it could be partially closing on you, and you may get a whistling sound from that