Thumping stereo feedback oddity (with exciting video!)

[Bear-n]

Anyone with any knowledge of what this might be? Can't be a bad speaker connection as it started at the F/R speaker - disappeared for a few weeks and then reappeared on a different speaker at the rear!

The sound is also ridiculously quiet as well, if that helps in any diagnosis.

Cheers for any thoughts or pointers.

https://youtu.be/oC6Loc-wwPM

[Bear-n]

Bump for any weekend folk?

Although it appears this bit of the forum is a lonely place!