Rear deraileur maintenance / adjustment
As mentioned in the other answer, the first thing that could be tried is adjusting the B-screw.  This adjustment will vary the gap between the jockey wheel and cassette. Clockwise rotation of the B-screw moves the jockey wheel away from the cassette, widening the gap between them.  Conversely, loosening the B-screw counterclockwise, will move the jockey wheel close to the cassette.  Proper position for setting the B-screw is when chain is on small chainwheel and large rear cog. Measuring from tooth tip to tooth tip there should be a 5-6 mm gap between jockey wheel and large cassette cog. An Allen key of 5mm should just squeeze through the gap is how I determine my adjustment. Even though your shifting seems unaffected, the jockey wheel should not interfere or touch the cassette in any way.