@robert1976 If 95% of the recordings sound fine, you are seeking a solution for the 5% that don’t. A solution that makes those 5% sound fine may adversely affect your satisfaction with the other 95%. I reiterate my view that a software or hardware approach to reducing treble energy for specific albums is a safe approach.
Acoustic treatments may help reduce the excess brightness and hash from those 5%, but they might unacceptably dampen the sound of the other 95%. Either try treatments that can be returned or consider hiring a capable acoustic engineer who knows how to treat a room.
I would also consider some of the highly cost effective, simple suggestions made by others - get a better Ethernet switch; try different Ethernet cables. Those, in particular, can make a very audible difference, but again those solutions affect everything, not just the objectionable 5%.
Good luck.