Exactly. That is part of the purpose of the steering diodes; parallel supply operation with increased current when demanded by the load.
Picture two or three supplies bussed together without steering diodes. Now consider a failure of one supply. Depending on the mode of failure of course, the other supply(s) could see another load and this could bring on a cascading failure. The primary purpose of steering diodes, among a few minor reasons, is to prevent cascading failure mode of redundant parallel sources by isolation via the reversed biased diode of the dead supply.
To isolate the offending supply, if it were me, I would physically disconnect one of the three supplies from the buss, light off the remaining two and check for the noise issue. Repeat this until the problem supply is determined by elimination.