I have not used a 5975T but I have seen this behavior on other 597x systems. All proved to be either a faulty multiplier or HED detector. The one exception was finding barely visible "lint" around the detector. Easily cleaned with a can of air. It does not look like chemical noise even though you see it on injection. You may not see it in Manual Tune just due to the y-scaling at 800,000 counts vs 70. Rerun Scan in Manual Tune with the PFTBA valve closed to reduce the response and the y-scale.