My machine has been a bit clunky and the tension hasn't been holding, I noticed at a bobbin change that there was some fluffy in the bobbin area. I debated about doing a quick clean or doing the full works and jerks for a couple of seconds... I only had half and hour before I had to go and pick the kids up from Nan's... Oh just do it properly... won out. This is what I found when I lifted the throat plate, glad I popped the lid for a looksee.
A couple of minutes to clean this out and a good oil around the bobbin case and I was good to go. It sounds like it has just been serviced, nice and quiet again and the tension is staying where it is put.