The IEC connectors on the aftermarket cables in my system were loose, too, and searching AudigoN for a solution brought me to this thread and one from a few years ago. The two most promising suggestions (aside from upgrading the connectors themselves) were adding shrink tubing or electrical tape to the male IEC connector.
Wanting to avoid the gooey mess the glue on electrical tape makes as it degrades sent me rummaging for some uber-sized shrink tubing bought for a long ago project. The tubing wasn't found, but the search lead me to what may be a good solution: Teflon tape. The same stuff plumbers use to keep screw on fittings from leaking. Well, supposedly Teflon is better than PVC in building cables and the tape has no glue. If the experiment didn't pan out removal would be easy and clean, so why not?
Carefully wrapping about 24" inches of tape around each male IEC connector, making sure to keep it away from the electrical end of things, worked like a charm. No more sagging IECs and what appears to be a more secure connection.
It could just be my mood or satisfaction from solving a puzzle (like my car being faster after I change the oil?), but after an hour the sound seemed a bit more relaxed. I'll check back if something more realistic crops up. The experiences of anyone else who gives this a try would be of interest.