04 gehl 6640 hydraulic noise

[04gehl]

I have a 04 gehl 6640 with 1600 hours the machine works great has full power but when the machine gets up to full operating temperature it starts to make a high pitched hydraulic squeal it only does it when turning to the left or when you are going in reverse it doesn't seem like a drive motor because I have full power to all wheels hydraulic oil recently changed and no junk in the filters. Could this be one of the two control valves that controls the direction steering and driving for the machine any help is appreciated thanks

 

[04gehl]

I have now had the tandem pump rebuilt was in pretty rough shape the drive motors were looked at but they were still in brand new condition I got the machine put back together this weekend and it drives like a brand new machine but still makes the squealing noise when it warms up the only thing I can think of that it could be now is the two speed and brake solenoid control valve

 

[Tazza]

I have now had the tandem pump rebuilt was in pretty rough shape the drive motors were looked at but they were still in brand new condition I got the machine put back together this weekend and it drives like a brand new machine but still makes the squealing noise when it warms up the only thing I can think of that it could be now is the two speed and brake solenoid control valve

Could the oil be a little too thin? when it heats up, it gets thinner, this could have been what damaged the pumps in the first place