Bernina virtuosa 155

Question

hi ive been having some problems with my machine, it has started sounding like its chugging and the bobbin sounds like its rattling a bit. i had this problem before and opened up the top and tightened some kind of arm holding the tension and oiled the bobbin area. it seemed to work again and hardly made a sound. but i have had to oil it several times each time i use it for that noise to go away and the stitches be even but now it is happening again, the stitches bunch up underneath and it sounds really bad! i live on a remote island and nobody here has heard of bernina i dont think so i have to do all repairs myself!please help!