I was all planned out yesterday, sew the darts, press, interface, overlocking, zip in, sew sides etc. I started stitching the darts and got that horrible clunky noise, I thought it was because I'd gone into reverse and hit air. Re-threaded, same thing happened, took the bottom out, cleaned, good blow out, re-thread paying a lot of attention managed until the last dart and started clunking again. So now I'm thinking I need another machine, which I hate because I then have to remember exactly how each one works, which is not as daft as it sounds really, different threading and bottom bits. After three or four complete re-threads I managed to get it done.
I finished up leaving when I'd got the overlocking done, I couldn't be bothered to fight to put the zip in. Later when I was wondering whether I might have a serious problem and it might be new machine time I was sort of wondering why it should happen when it is such flipping steady teddy other times. Then I had a lightbulb moment. Looking for the thread, if I don't get a match I don't bother as I use Gutermann Mara 120, but this time I'd found a match, but it was two reels of some old Coats that I'd bought that came with a job lot of Gutermann threads.
So is this the problem? I have had it occasionally before, solved by re-theading and that was it, soldiered on as usual.