Screw compressor issues

Hi guys, I'm a first time poster here so hope I'm posting this in the right place. I've been working on an air cooled Ciat chiller the last couple of days. Has a bitzer screw compressor type CSH7571-90Y. I was carrying out repairs to a leaking plug on the bottom of the compressor. Oil was drained from compressor during work and filled back up again afterwards to the correct level in the sight glass, just above halfway. Upon recommissioning I noticed that the compressor was really noisy, runs louder than the same compressor in an adjacent chiller, screams a little bit and has a high pitched whine in the background. It also vibrates at a frequency that resonates throughout the casing of the chiller. When I checked the sight glass the oil level has dropped just below the level of the sight glass and looked as if it was spraying around inside . I'm pretty sure it's not foaming and I measured decent superheats, between 5 and 9k. Looks more like it is being disturbed mechanically. Could this just be because the oil level is low enough for me to see it being whipped around inside or could it be something else? Also, why has my oil level dropped so low. It seems to maintain at a level just below or just on the bottom of the sight glass. There is no external oil separator or oil line on the chiller so just relies on velocity through refrigerant circuit for oil return. Any help would be much appreciated, cheers!

Hi paddy it's mechanical noise , the bearings may need changing,

Do the other compressors have a stable oil level in sight glass?
Just considering if oil level high or low.
If high it could effect noise level, so if turned or cycled off, is oil level still same as you filled it?
If there is an oil filter it could be checked for debris, or even an oil analysis could be performed to determine condition of compressor & bearings.

Hi Paddy.
Welcome to the forum.

Please pay attention to all of the above as it is all relevant.

However you may like to charge the sight glass to say 3/4 sight glass and then run the comp.

A drained compressor, particularly when having been standing.
Will always loose oil level (as shown in the sight glass!) as it restarts.
This is because all the oil galleries etc. will need to be recharged.
So top up some more and observe.
The resonance from the comp may improve and level stabilise?

If all is the same them start investigating the afor recommended.

Good luck all the same.
Grizzly

Yea, the other compressors have stable oil levels, all around 1/2 to 2/3. When cycles off the oil level sits just below 1/4 of the sight glass, so below where I filled it to. I may attempt to top levels up as recommended by grizzly. Thanks for the advice.