Hi Alto. I agree you have a plausible explanation for some situations, but it unfortunately isn't the case at Seeb Tower. They are using headsets, and it IS a known issue - for years.
The only reason I can come up with is there is some fault in a minority of the controller's PTT (Push To Talk) buttons, and that sets up some type of feed-back. It's not all of the time, but when it happens, its usually with one controller, and the sound is truly sonic-blast-loud!
I've heard complaints from EK, British Airways, Qatar, Gulfair, Indian, Lufthansa, and the good-ol' home-town boys, Oman Air. The controllers even go as far to get a complaint confirmed by other aircraft right there and then, and they all have agreed it is loud.
This isn't the remote-transceiver issue the Centre has had for a while...that is a separate issue. This is is JUST at the Tower.
With such surplus cash Oman is reaping from the over-priced petroleum-products recently, how about you guys at Seeb GET YOUR RADIOS FIXED!!