Foggy Notion

'I've been tired' - The Pixies

Just ruminating.... our lead guitarist had a similar issue with his Les Paul Standard. The 'PINGING' was the clue here, he had the same. After going through the same sequence workarounds as explained in the above posts it seems the culprit was a combination of high break angle over the bridge & bridge saddles that needed lubricating. If break angle over the saddles is too steep then strings, especially wound strings, may be dragging/catching. Worth a try to adjust the stop tail height & lube the saddles, 10 min job. FWIW, when stretching out new strings, make sure that you stretch the WHOLE string, not just the bit that goes between the nut & bridge.