Bobcat high pitch whine

Have a 2017 Bobcat S70 (only 200 hours) with a high pitched hydraulic whine at about 1/4 throttle and higher. Everything on the machine works as it should....except for the odd whine. I changed the hydro oil and filter...which silenced the noise for roughly an hour....but now is back. The only time the noise subsides is when the lift arms are LOWERED. No leaks, checked all hose clamps, fittings etc. The hydro oil filter and bottom plate have a good amount of vibration when the high pitch whine occurs....and I believe I've narrowed the noise is coming from roughly that area of the machine......

Ideas????

Warranty still good?

No....they only come with a 1 year warranty....

Are you checking hyd oil level with boom and blade in correct position?

Yes....with all cylinders retracted. Hydro level is good...no air bubbles in oil either...

I don't have much experience with BC but the older models like the T-190, S220 and the like, that hyd. whine always occurred when it was going over relief. Which on the T-190 started when it looked at going into a pile. When I read your post that was what came to mind, it sounds like the machine is going over relief. Maybe a valve is stuck and causing that to occur. It is just thought, and I don't know how to easily check for that.

So temperature today was 55ish and I briefly used the machine today (20 minutes) and there was NO WHINE.....so obviously flow and temperature have something to do with this issue. The noise always happens when it's colder out....as I primarily use this machine for sidewalk snow removal with a snow plow on it. The noise DOES NOT getting quieter after the unit is warmed up (when it's cold out)......so I'm baffled!

Usually a hydraulic whine is due to the pump starving for oil. The fact that it subsides when the oil is warm (and thinner) makes this case even stronger. I'm not familiar with this machine in particular but if I was chasing it I'd start at the pump and trace the supply line back to the tank. See if a hose is kinked or steel line crushed. Is there a screen on the oil pickup tube before the filter? I'd be looking for anything that might restrict oil flow to the pump.