Schiit Freya + emits a high pitch squeal when using tube stage

Hello,

Bought my Freya + back in April 2020. I mainly use the tube stage. After a few months of use (total of less than 30 hours of use), I started hearing a low volume, high pitch squeal coming from an area around the tubes after an hour or so of listening. I swapped the tubes around and it didn't resolve the issue. If I switch to passive or JFET stage the squealing sound is no longer present. I contacted Schiit and they had me send the unit back (without the tubes as they told me to exclude them) for repair. I received the unit back with a note stating they fixed the problem and burned the unit in. After several hours of using the unit again, the noise is back. Has anyone experience this with their unit? I don't want to pay to ship the unit back to Schiit a second time.