8070 hydraulic air/chatter

Hello, I have a 8070 that occasionally makes a chattering/fizzing noise through the hydraulic system. It sounds like it is coming from the remote valve stack under the back of the cab area. Its not a hammering chatter, but more of a fizzing sound (foaming?). If I were to picture what is happening, I would say there is a air/foam pocket in the right filter housing and its sending small air bubbles through the piston pump. It rarely if ever happens at low engine speed. It happens more with road travel (higher temp?). It can but not always be triggered by hitting a bump. The funny things is if it's a air pocket I would think there would be a delay from hitting a bump to it making its way through the pump to the valve stack. But it's usually instantly, hit a bump and it triggers the fizzing. It's slowly getting more common to where it is a concern. Cycling the remote or 3pt lever or pressing a brake pedal usually makes it go away for a little bit.

I know about the possibility of hoses grounding out on the cab and I have check that. I've check the priority valve on the gear pump. It seems fine and moves free.

The oil level is normal and factory 821 oil (and has been changed). Also the filters have been changed. I also know about dirty sight glasses, they are clear. I have considered something wrong with the left hand filter check valve not opening (starving the gear pump) but it seems to be fine. Steering operates fine also. Really no complaints of any operation in hydraulics. Just this noise is becoming more common.

I have thought of suction line leaks but if air could get in wouldn't oil leak out when it's not running. The only visible leak is some small drops hanging off the piston pump compensator adjusting screw caps.

So my two questions are.
What could be causing this?
How is air suppose to purge from the piston pump circuit (the path)?

Thanks

wekracer wrote: I don't have a answer to your question but I know what your talking about. We have an 8070 8050 and an 8010 and they all do the same thing. Usually on start up too when I raise the implement it will stop raising while the chattering is happening.

Sounds a lot like my 7045.

I think from the beginning of the new flow/pressure compensated hydraulic system on a 7030/7050 thru the last 8070 built, there have been noises like this and I consider them "normal" as long as the hydraulics perform when asked to. Remember, this system is located below oil level because it really doesn't have a true "charge" pump to force-feed supply oil to the main piston pump. Cold oil temps make it even more noticeable because of this. It's just the way it is.