As has been mentioned earlier the metal dots on the impeller are balance weights, just like the small lead weights that are placed on car wheels to balance them. They have always been a fundamental part of the design even before the D5 existed, in the d4 generation pumps. Every impeller has them in different places and number, installed by Xylem.
Without being able to examine the pump it's impossible to know what the problem actually is.
If old mate in the video has never seen balance weights before and could not tell that all the pumps in front of him have them then I can't say that gives me much confidence in any analysis he might provide.
Last edited by Ashcroft; 05-07-2019 at 06:26 PM.